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A History of Science, Volume 4

by Henry Smith Williams

April, 1999  [Etext #1708]


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A History of Science, Volume 1, by Henry Smith Williams

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A HISTORY OF SCIENCE
BY
HENRY SMITH WILLIAMS, M.D., LL.D.
ASSISTED BY
EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES
VOLUME IV.

MODERN DEVELOPMENT OF THE
CHEMICAL AND BIOLOGICAL SCIENCES




A HISTORY OF SCIENCE

BOOK IV

MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES

AS regards chronology, the epoch covered in the present volume is
identical with that viewed in the preceding one. But now as
regards subject matter we pass on to those diverse phases of the
physical world which are the field of the chemist, and to those
yet more intricate processes which have to do with living
organisms.  So radical are the changes here that we seem to be
entering new worlds; and yet, here as before, there are
intimations of the new discoveries away back in the Greek days.
The solution of the problem of respiration will remind us that
Anaxagoras half guessed the secret; and in those diversified
studies which tell us of the Daltonian atom in its wonderful
transmutations, we shall be reminded again of the Clazomenian
philosopher and his successor Democritus.

Yet we should press the analogy much too far were we to intimate
that the Greek of the elder day or any thinker of a more recent
period had penetrated, even in the vaguest way, all of the
mysteries that the nineteenth century has revealed in the fields
of chemistry and biology.  At the very most the insight of those
great Greeks and of the wonderful seventeenth-century
philosophers who so often seemed on the verge of our later
discoveries did no more than vaguely anticipate their successors
of this later century. To gain an accurate, really specific
knowledge of the properties of elementary bodies was reserved for
the chemists of a recent epoch. The vague Greek questionings as
to organic evolution were world-wide from the precise inductions
of a Darwin.  If the mediaeval Arabian endeavored to dull the
knife of the surgeon with the use of drugs, his results hardly
merit to be termed even an anticipation of modern anaesthesia.
And when we speak of preventive medicine--of bacteriology in all
its phases--we have to do with a marvellous field of which no
previous generation of men had even the slightest inkling.

All in all, then, those that lie before us are perhaps the most
wonderful and the most fascinating of all the fields of science.
As the chapters of the preceding book carried us out into a
macrocosm of inconceivable magnitude, our present studies are to
reveal a microcosm of equally inconceivable smallness. As the
studies of the physicist attempted to reveal the very nature of
matter and of energy, we have now to seek the solution of the yet
more inscrutable problems of life and of mind.



I. THE PHLOGISTON THEORY IN CHEMISTRY

The development of the science of chemistry from the "science" of
alchemy is a striking example of the complete revolution in the
attitude of observers in the field of science. As has been
pointed out in a preceding chapter, the alchemist, having a
preconceived idea of how things should be, made all his
experiments to prove his preconceived theory; while the chemist
reverses this attitude of mind and bases his conceptions on the
results of his laboratory experiments. In short, chemistry is
what alchemy never could be, an inductive science.  But this
transition from one point of view to an exactly opposite one was
necessarily a very slow process. Ideas that have held undisputed
sway over the minds of succeeding generations for hundreds of
years cannot be overthrown in a moment, unless the agent of such
an overthrow be so obvious that it cannot be challenged.  The
rudimentary chemistry that overthrew alchemy had nothing so
obvious and palpable.

The great first step was the substitution of the one principle,
phlogiston, for the three principles, salt, sulphur, and mercury.
We have seen how the experiment of burning or calcining such a
metal as lead "destroyed" the lead as such, leaving an entirely
different substance in its place, and how the original metal
could be restored by the addition of wheat to the calcined
product. To the alchemist this was "mortification" and
"revivification" of the metal.  For, as pointed out by
Paracelsus, "anything that could be killed by man could also be
revivified by him, although this was not possible to the things
killed by God."  The burning of such substances as wood, wax,
oil, etc., was also looked upon as the same "killing" process,
and the fact that the alchemist was unable to revivify them was
regarded as simply the lack of skill on his part, and in no wise
affecting the theory itself.

But the iconoclastic spirit, if not the acceptance of all the
teachings, of the great Paracelsus had been gradually taking root
among the better class of alchemists, and about the middle of the
seventeenth century Robert Boyle (1626-1691) called attention to
the possibility of making a wrong deduction from the phenomenon
of the calcination of the metals, because of a very important
factor, the action of the air, which was generally overlooked. 
And he urged his colleagues of the laboratories to give greater
heed to certain other phenomena that might pass unnoticed in the
ordinary calcinating process. In his work, The Sceptical Chemist,
he showed the reasons for doubting the threefold constitution of
matter; and in his General History of the Air advanced some novel
and carefully studied theories as to the composition of the
atmosphere. This was an important step, and although Boyle is not
directly responsible for the phlogiston theory, it is probable
that his experiments on the atmosphere influenced considerably
the real founders, Becker and Stahl.

Boyle gave very definitely his idea of how he thought air might
be composed. "I conjecture that the atmospherical air consists of
three different kinds of corpuscles," he says; "the first, those
numberless particles which, in the form of vapors or dry
exhalations, ascend from the earth, water, minerals, vegetables,
animals, etc.; in a word, whatever substances are elevated by the
celestial or subterraneal heat, and thence diffused into the
atmosphere.  The second may be yet more subtle, and consist of
those exceedingly minute atoms, the magnetical effluvia of the
earth, with other innumerable particles sent out from the bodies
of the celestial luminaries, and causing, by their influence, the
idea of light in us.  The third sort is its characteristic and
essential property, I mean permanently elastic parts. Various
hypotheses may be framed relating to the structure of these later
particles of the air.  They might be resembled to the springs of
watches, coiled up and endeavoring to restore themselves; to
wool, which, being compressed, has an elastic force; to slender
wires of different substances, consistencies, lengths, and
thickness; in greater curls or less, near to, or remote from each
other, etc., yet all continuing springy, expansible, and
compressible. Lastly, they may also be compared to the thin
shavings of different kinds of wood, various in their lengths,
breadth, and thickness. And this, perhaps, will seem the most
eligible hypothesis, because it, in some measure, illustrates the
production of the elastic particles we are considering.  For no
art or curious instruments are required to make these shavings
whose curls are in no wise uniform, but seemingly casual; and
what is more remarkable, bodies that before seemed unelastic, as
beams and blocks, will afford them."[1]

Although this explanation of the composition of the air is most
crude, it had the effect of directing attention to the fact that
the atmosphere is not "mere nothingness," but a "something" with
a definite composition, and this served as a good foundation for
future investigations.  To be sure, Boyle was neither the first
nor the only chemist who had suspected that the air was a mixture
of gases, and not a simple one, and that only certain of these
gases take part in the process of calcination.  Jean Rey, a
French physician, and John Mayow, an Englishman, had preformed
experiments which showed conclusively that the air was not a
simple substance; but Boyle's work was better known, and in its
effect probably more important. But with all Boyle's explanations
of the composition of air, he still believed that there was an
inexplicable something, a "vital substance," which he was unable
to fathom, and which later became the basis of Stahl's phlogiston
theory. Commenting on this mysterious substance, Boyle says:
"The, difficulty we find in keeping flame and fire alive, though
but for a little time, without air, renders it suspicious that
there be dispersed through the rest of the atmosphere some odd
substance, either of a solar, astral, or other foreign nature; on
account of which the air is so necessary to the substance of
flame!" It was this idea that attracted the attention of George
Ernst Stahl (1660-1734), a professor of medicine in the
University of Halle, who later founded his new theory upon it. 
Stahl's theory was a development of an earlier chemist, Johann
Joachim Becker (1635-1682), in whose footsteps he followed and
whose experiments he carried further.

In many experiments Stahl had been struck with the fact that
certain substances, while differing widely, from one another in
many respects, were alike in combustibility. From this he argued
that all combustible substances must contain a common principle,
and this principle he named phlogiston. This phlogiston he
believed to be intimately associated in combination with other
substances in nature, and in that condition not perceivable by
the senses; but it was supposed to escape as a substance burned,
and become apparent to the senses as fire or flame. In other
words, phlogiston was something imprisoned in a combustible
structure (itself forming part of the structure), and only
liberated when this structure was destroyed. Fire, or flame, was
FREE phlogiston, while the imprisoned phlogiston was called
COMBINED PHLOGISTON, or combined fire. The peculiar quality of
this strange substance was that it disliked freedom and was
always striving to conceal itself in some combustible substance. 
Boyle's tentative suggestion that heat was simply motion was
apparently not accepted by Stahl, or perhaps it was unknown to
him.

According to the phlogistic theory, the part remaining after a
substance was burned was simply the original substance deprived
of phlogiston. To restore the original combustible substance, it
was necessary to heat the residue of the combustion with
something that burned easily, so that the freed phlogiston might
again combine with the ashes. This was explained by the
supposition that the more combustible a substance was the more
phlogiston it contained, and since free phlogiston sought always
to combine with some suitable substance, it was only necessary to
mix the phlogisticating agents, such as charcoal, phosphorus,
oils, fats, etc., with the ashes of the original substance, and
heat the mixture, the phlogiston thus freed uniting at once with
the ashes.  This theory fitted very nicely as applied to the
calcined lead revivified by the grains of wheat, although with
some other products of calcination it did not seem to apply at
all.

It will be seen from this that the phlogistic theory was a step
towards chemistry and away from alchemy.  It led away from the
idea of a "spirit" in metals that could not be seen, felt, or
appreciated by any of the senses, and substituted for it a
principle which, although a falsely conceived one, was still much
more tangible than the "spirit," since it could be seen and felt
as free phlogiston and weighed and measured as combined
phlogiston. The definiteness of the statement that a metal, for
example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist
that "metals are produced by the spiritual action of the three
principles, salt, mercury, sulphur"--particularly when it is
explained that salt, mercury, and sulphur were really not what
their names implied, and that there was no universally accepted
belief as to what they really were.

The metals, which are now regarded as elementary bodies, were
considered compounds by the phlogistians, and they believed that
the calcining of a metal was a process of simplification. They
noted, however, that the remains of calcination weighed more than
the original product, and the natural inference from this would
be that the metal must have taken in some substance rather than
have given off anything.  But the phlogistians had not learned
the all-important significance of weights, and their explanation
of variation in weight was either that such gain or loss was an
unimportant "accident" at best, or that phlogiston, being light,
tended to lighten any substance containing it, so that driving it
out of the metal by calcination naturally left the residue
heavier.

At first the phlogiston theory seemed to explain in an
indisputable way all the known chemical phenomena.  Gradually,
however, as experiments multiplied, it became evident that the
plain theory as stated by Stahl and his followers failed to
explain satisfactorily certain laboratory reactions.  To meet
these new conditions, certain modifications were introduced from
time to time, giving the theory a flexibility that would allow it
to cover all cases. But as the number of inexplicable experiments
continued to increase, and new modifications to the theory became
necessary, it was found that some of these modifications were
directly contradictory to others, and thus the simple theory
became too cumbersome from the number of its modifications. Its
supporters disagreed among themselves, first as to the
explanation of certain phenomena that did not seem to accord with
the phlogistic theory, and a little later as to the theory
itself.  But as yet there was no satisfactory substitute for this
theory, which, even if unsatisfactory, seemed better than
anything that had gone before or could be suggested.

But the good effects of the era of experimental research, to
which the theory of Stahl had given such an impetus, were showing
in the attitude of the experimenters. The works of some of the
older writers, such as Boyle and Hooke, were again sought out in
their dusty corners and consulted, and their surmises as to the
possible mixture of various gases in the air were more carefully
considered.  Still the phlogiston theory was firmly grounded in
the minds of the philosophers, who can hardly be censured for
adhering to it, at least until some satisfactory substitute was
offered.  The foundation for such a theory was finally laid, as
we shall see presently, by the work of Black, Priestley,
Cavendish, and Lavoisier, in the eighteenth century, but the
phlogiston theory cannot be said to have finally succumbed until
the opening years of the nineteenth century.



II. THE BEGINNINGS OF MODERN CHEMISTRY

THE "PNEUMATIC" CHEMISTS

Modern chemistry may be said to have its beginning with the work
of Stephen Hales (1677-1761), who early in the eighteenth century
began his important study of the elasticity of air. Departing
from the point of view of most of the scientists of the time, be
considered air to be "a fine elastic fluid, with particles of
very different nature floating in it" ; and he showed that these
"particles" could be separated. He pointed out, also, that
various gases, or "airs," as he called them, were contained in
many solid substances. The importance of his work, however, lies
in the fact that his general studies were along lines leading
away from the accepted doctrines of the time, and that they gave
the impetus to the investigation of the properties of gases by
such chemists as Black, Priestley, Cavendish, and Lavoisier,
whose specific discoveries are the foundation-stones of modern
chemistry.


JOSEPH BLACK

The careful studies of Hales were continued by his younger
confrere, Dr. Joseph Black (1728-1799), whose experiments in the
weights of gases and other chemicals were first steps in
quantitative chemistry. But even more important than his
discoveries of chemical properties in general was his discovery
of the properties of carbonic-acid gas.

Black had been educated for the medical profession in the
University of Glasgow, being a friend and pupil of the famous Dr.
William Cullen.  But his liking was for the chemical laboratory
rather than for the practice of medicine.  Within three years
after completing his medical course, and when only twenty-three
years of age, he made the discovery of the properties of carbonic
acid, which he called by the name of "fixed air."  After
discovering this gas, Black made a long series of experiments, by
which he was able to show how widely it was distributed
throughout nature.  Thus, in 1757, be discovered that the bubbles
given off in the process of brewing, where there was vegetable
fermentation, were composed of it. To prove this, he collected
the contents of these bubbles in a bottle containing lime-water.
When this bottle was shaken violently, so that the lime-water and
the carbonic acid became thoroughly mixed, an insoluble white
powder was precipitated from the solution, the carbonic acid
having combined chemically with the lime to form the insoluble
calcium carbonate, or chalk.  This experiment suggested another.
Fixing a piece of burning charcoal in the end of a bellows, he
arranged a tube so that the gas coming from the charcoal would
pass through the lime-water, and, as in the case of the bubbles
from the brewer's vat, he found that the white precipitate was
thrown down; in short, that carbonic acid was given off in
combustion. Shortly after, Black discovered that by blowing
through a glass tube inserted into lime-water, chalk was
precipitated, thus proving that carbonic acid was being
constantly thrown off in respiration.

The effect of Black's discoveries was revolutionary, and the
attitude of mind of the chemists towards gases, or "airs," was
changed from that time forward. Most of the chemists, however,
attempted to harmonize the new facts with the older theories--to
explain all the phenomena on the basis of the phlogiston theory,
which was still dominant. But while many of Black's discoveries
could not be made to harmonize with that theory, they did not
directly overthrow it. It required the additional discoveries of
some of Black's fellow-scientists to complete its downfall, as we
shall see.


HENRY CAVENDISH

This work of Black's was followed by the equally important work
of his former pupil, Henry Cavendish (1731-1810), whose discovery
of the composition of many substances, notably of nitric acid and
of water, was of great importance, adding another link to the
important chain of evidence against the phlogiston theory.
Cavendish is one of the most eccentric figures in the history of
science, being widely known in his own time for his immense
wealth and brilliant intellect, and also for his peculiarities
and his morbid sensibility, which made him dread society, and
probably did much in determining his career. Fortunately for him,
and incidentally for the cause of science, he was able to pursue
laboratory investigations without being obliged to mingle with
his dreaded fellow-mortals, his every want being provided for by
the immense fortune inherited from his father and an uncle.

When a young man, as a pupil of Dr. Black, he had become imbued
with the enthusiasm of his teacher, continuing Black's
investigations as to the properties of carbonic-acid gas when
free and in combination. One of his first investigations was
reported in 1766, when he communicated to the Royal Society his
experiments for ascertaining the properties of carbonic-acid and
hydrogen gas, in which he first showed the possibility of
weighing permanently elastic fluids, although Torricelli had
before this shown the relative weights of a column of air and a
column of mercury. Other important experiments were continued by
Cavendish, and in 1784 he announced his discovery of the
composition of water, thus robbing it of its time-honored
position as an "element." But his claim to priority in this
discovery was at once disputed by his fellow-countryman James
Watt and by the Frenchman Lavoisier. Lavoisier's claim was soon
disallowed even by his own countrymen, but for many years a
bitter controversy was carried on by the partisans of Watt and
Cavendish.  The two principals, however, seem. never to have
entered into this controversy with anything like the same ardor
as some of their successors, as they remained on the best of
terms.[1] It is certain, at any rate, that Cavendish announced
his discovery officially before Watt claimed that the
announcement had been previously made by him, "and, whether right
or wrong, the honor of scientific discoveries seems to be
accorded naturally to the man who first publishes a demonstration
of his discovery." Englishmen very generally admit the justness
of Cavendish's claim, although the French scientist Arago, after
reviewing the evidence carefully in 1833, decided in favor of
Watt.

It appears that something like a year before Cavendish made known
his complete demonstration of the composition of water, Watt
communicated to the Royal Society a suggestion that water was
composed of "dephlogisticated air (oxygen) and phlogiston
(hydrogen) deprived of part of its latent heat." Cavendish knew
of the suggestion, but in his experiments refuted the idea that
the hydrogen lost any of its latent heat. Furthermore, Watt
merely suggested the possible composition without proving it,
although his idea was practically correct, if we can rightly
interpret the vagaries of the nomenclature then in use. But had
Watt taken the steps to demonstrate his theory, the great "Water
Controversy" would have been avoided. Cavendish's report of his
discovery to the Royal Society covers something like forty pages
of printed matter. In this he shows how, by passing an electric
spark through a closed jar containing a mixture of hydrogen gas
and oxygen, water is invariably formed, apparently by the union
of the two gases. The experiment was first tried with hydrogen
and common air, the oxygen of the air uniting with the hydrogen
to form water, leaving the nitrogen of the air still to be
accounted for. With pure oxygen and hydrogen, however, Cavendish
found that pure water was formed, leaving slight traces of any
other, substance which might not be interpreted as being Chemical
impurities. There was only one possible explanation of this
phenomenon--that hydrogen and oxygen, when combined, form water.

"By experiments with the globe it appeared," wrote Cavendish,
"that when inflammable and common air are exploded in a proper
proportion, almost all the inflammable air, and near one-fifth
the common air, lose their elasticity and are condensed into dew.
And by this experiment it appears that this dew is plain water,
and consequently that almost all the inflammable air is turned
into pure water.

"In order to examine the nature of the matter condensed on firing
a mixture of dephlogisticated and inflammable air, I took a glass
globe, holding 8800 grain measures, furnished with a brass cock
and an apparatus for firing by electricity.  This globe was well
exhausted by an air-pump, and then filled with a mixture of
inflammable and dephlogisticated air by shutting the cock,
fastening the bent glass tube into its mouth, and letting up the
end of it into a glass jar inverted into water and containing a
mixture of 19,500 grain measures of dephlogisticated air, and
37,000 of inflammable air; so that, upon opening the cock, some
of this mixed air rushed through the bent tube and filled the
globe. The cock was then shut and the included air fired by
electricity, by means of which almost all of it lost its
elasticity (was condensed into water vapors). The cock was then
again opened so as to let in more of the same air to supply the
place of that destroyed by the explosion, which was again fired,
and the operation continued till almost the whole of the mixture
was let into the globe and exploded.  By this means, though the
globe held not more than a sixth part of the mixture, almost the
whole of it was exploded therein without any fresh exhaustion of
the globe."

At first this condensed matter was "acid to the taste and
contained two grains of nitre," but Cavendish, suspecting that
this was due to impurities, tried another experiment that proved
conclusively that his opinions were correct. "I therefore made
another experiment," he says, "with some more of the same air
from plants in which the proportion of inflammable air was
greater, so that the burnt air was almost completely
phlogisticated, its standard being one-tenth. The condensed
liquor was then not at all acid, but seemed pure water."

From these experiments he concludes "that when a mixture of
inflammable and dephlogisticated air is exploded, in such
proportions that the burnt air is not much phlogisticated, the
condensed liquor contains a little acid which is always of the
nitrous kind, whatever substance the dephlogisticated air is
procured from; but if the proportion be such that the burnt air
is almost entirely phlogisticated, the condensed liquor is not at
all acid, but seems pure water, without any addition
whatever."[2]

These same experiments, which were undertaken to discover the
composition of water, led him to discover also the composition of
nitric acid. He had observed that, in the combustion of hydrogen
gas with common air, the water was slightly tinged with acid, but
that this was not the case when pure oxygen gas was used.  Acting
upon this observation, he devised an experiment to determine the
nature of this acid. He constructed an apparatus whereby an
electric spark was passed through a vessel containing common air. 
After this process had been carried on for several weeks a small
amount of liquid was formed. This liquid combined with a solution
of potash to form common nitre, which "detonated with charcoal,
sparkled when paper impregnated with it was burned, and gave out
nitrous fumes when sulphuric acid was poured on it."  In other
words, the liquid was shown to be nitric acid. Now, since nothing
but pure air had been used in the initial experiment, and since
air is composed of nitrogen and oxygen, there seemed no room to
doubt that nitric acid is a combination of nitrogen and oxygen.

This discovery of the nature of nitric acid seems to have been
about the last work of importance that Cavendish did in the field
of chemistry, although almost to the hour of his death he was
constantly occupied with scientific observations.  Even in the
last moments of his life this habit asserted itself, according to
Lord Brougham.  "He died on March 10, 1810, after a short
illness, probably the first, as well as the last, which he ever
suffered. His habit of curious observation continued to the end.
He was desirous of marking the progress of the disease and the
gradual extinction of the vital powers.  With these ends in view,
that he might not be disturbed, he desired to be left alone. His
servant, returning sooner than he had wished, was ordered again
to leave the chamber of death, and when be came back a second
time he found his master had expired.[3]


JOSEPH PRIESTLEY

While the opulent but diffident Cavendish was making his
important discoveries, another Englishman, a poor country
preacher named Joseph Priestley (1733-1804) was not only
rivalling him, but, if anything, outstripping him in the pursuit
of chemical discoveries. In 1761 this young minister was given a
position as tutor in a nonconformist academy at Warrington, and
here, for six years, he was able to pursue his studies in
chemistry and electricity. In 1766, while on a visit to London,
he met Benjamin Franklin, at whose suggestion he published his
History of Electricity.  From this time on he made steady
progress in scientific investigations, keeping up his
ecclesiastical duties at the same time. In 1780 he removed to
Birmingham, having there for associates such scientists as James
Watt, Boulton, and Erasmus Darwin.

Eleven years later, on the anniversary of the fall of the Bastile
in Paris, a fanatical mob, knowing Priestley's sympathies with
the French revolutionists, attacked his house and chapel, burning
both and destroying a great number of valuable papers and
scientific instruments. Priestley and his family escaped violence
by flight, but his most cherished possessions were destroyed; and
three years later he quitted England forever, removing to the
United States, whose struggle for liberty he had championed. The
last ten years of his life were spent at Northumberland,
Pennsylvania, where he continued his scientific researches.

Early in his scientific career Priestley began investigations
upon the "fixed air" of Dr. Black, and, oddly enough, he was
stimulated to this by the same thing that had influenced
Black--that is, his residence in the immediate neighborhood of a
brewery. It was during the course of a series of experiments on
this and other gases that he made his greatest discovery, that of
oxygen, or "dephlogisticated air," as he called it. The story of
this important discovery is probably best told in Priestley's own
words:

"There are, I believe, very few maxims in philosophy that have
laid firmer hold upon the mind than that air, meaning atmospheric
air, is a simple elementary substance, indestructible and
unalterable, at least as much so as water is supposed to be.  In
the course of my inquiries I was, however, soon satisfied that
atmospheric air is not an unalterable thing; for that, according
to my first hypothesis, the phlogiston with which it becomes
loaded from bodies burning in it, and the animals breathing it,
and various other chemical processes, so far alters and depraves
it as to render it altogether unfit for inflammation,
respiration, and other purposes to which it is subservient; and I
had discovered that agitation in the water, the process of
vegetation, and probably other natural processes, restore it to
its original purity....

"Having procured a lens of twelve inches diameter and twenty
inches local distance, I proceeded with the greatest alacrity, by
the help of it, to discover what kind of air a great variety of
substances would yield, putting them into the vessel, which I
filled with quicksilver, and kept inverted in a basin of the same
.... With this apparatus, after a variety of experiments .... on
the 1st of August, 1774, I endeavored to extract air from
mercurius calcinatus per se; and I presently found that, by means
of this lens, air was expelled from it very readily. Having got
about three or four times as much as the bulk of my materials, I
admitted water to it, and found that it was not imbibed by it.
But what surprised me more than I can express was that a candle
burned in this air with a remarkably vigorous flame, very much
like that enlarged flame with which a candle burns in nitrous
oxide, exposed to iron or liver of sulphur; but as I had got
nothing like this remarkable appearance from any kind of air
besides this particular modification of vitrous air, and I knew
no vitrous acid was used in the preparation of mercurius
calcinatus, I was utterly at a loss to account for it."[4]


The "new air" was, of course, oxygen.  Priestley at once
proceeded to examine it by a long series of careful experiments,
in which, as will be seen, he discovered most of the remarkable
qualities of this gas. Continuing his description of these
experiments, he says:

"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a
piece of red-hot wood sparkled in it, exactly like paper dipped
in a solution of nitre, and it consumed very fast; an experiment
that I had never thought of trying with dephlogisticated nitrous
air.

". . . I had so little suspicion of the air from the mercurius
calcinatus, etc., being wholesome, that I had not even thought of
applying it to the test of nitrous air; but thinking (as my
reader must imagine I frequently must have done) on the candle
burning in it after long agitation in water, it occurred to me at
last to make the experiment; and, putting one measure of nitrous
air to two measures of this air, I found not only that it was
diminished, but that it was diminished quite as much as common
air, and that the redness of the mixture was likewise equal to a
similar mixture of nitrous and common air.... The next day I was
more surprised than ever I had been before with finding that,
after the above-mentioned mixture of nitrous air and the air from
mercurius calcinatus had stood all night, . . . a candle burned
in it, even better than in common air."

A little later Priestley discovered that "dephlogisticated air .
. . is a principal element in the composition of acids, and may
be extracted by means of heat from many substances which contain
them.... It is likewise produced by the action of light upon
green vegetables; and this seems to be the chief means employed
to preserve the purity of the atmosphere."

This recognition of the important part played by oxygen in the
atmosphere led Priestley to make some experiments upon mice and
insects, and finally upon himself, by inhalations of the pure
gas.  "The feeling in my lungs," he said, "was not sensibly
different from that of common air, but I fancied that my
breathing felt peculiarly light and easy for some time
afterwards. Who can tell but that in time this pure air may
become a fashionable article in luxury? . . . Perhaps we may from
these experiments see that though pure dephlogisticated air might
be useful as a medicine, it might not be so proper for us in the
usual healthy state of the body."

This suggestion as to the possible usefulness of oxygen as a
medicine was prophetic.  A century later the use of oxygen had
become a matter of routine practice with many physicians. Even in
Priestley's own time such men as Dr. John Hunter expressed their
belief in its efficacy in certain conditions, as we shall see,
but its value in medicine was not fully appreciated until several
generations later.

Several years after discovering oxygen Priestley thus summarized
its properties:  "It is this ingredient in the atmospheric air
that enables it to support combustion and animal life. By means
of it most intense heat may be produced, and in the purest of it
animals will live nearly five times as long as in an equal
quantity of atmospheric air.  In respiration, part of this air,
passing the membranes of the lungs, unites with the blood and
imparts to it its florid color, while the remainder, uniting with
phlogiston exhaled from venous blood, forms mixed air. It is
dephlogisticated air combined with water that enables fishes to
live in it."[5]


KARL WILHELM SCHEELE

The discovery of oxygen was the last but most important blow to
the tottering phlogiston theory, though Priestley himself would
not admit it. But before considering the final steps in the
overthrow of Stahl's famous theory and the establishment of
modern chemistry, we must review the work of another great
chemist, Karl Wilhelm Scheele (1742-1786), of Sweden, who
discovered oxygen quite independently, although later than
Priestley.  In the matter of brilliant discoveries in a brief
space of time Scheele probably eclipsed all his great
contemporaries. He had a veritable genius for interpreting
chemical reactions and discovering new substances, in this
respect rivalling Priestley himself. Unlike Priestley, however,
he planned all his experiments along the lines of definite
theories from the beginning, the results obtained being the
logical outcome of a predetermined plan.

Scheele was the son of a merchant of Stralsund, Pomerania, which
then belonged to Sweden.  As a boy in school he showed so little
aptitude for the study of languages that he was apprenticed to an
apothecary at the age of fourteen.  In this work he became at
once greatly interested, and, when not attending to his duties in
the dispensary, he was busy day and night making experiments or
studying books on chemistry. In 1775, still employed as an
apothecary, he moved to Stockholm, and soon after he sent to
Bergman, the leading chemist of Sweden, his first discovery--that
of tartaric acid, which he had isolated from cream of tartar.
This was the beginning of his career of discovery, and from that
time on until his death he sent forth accounts of new discoveries
almost uninterruptedly. Meanwhile he was performing the duties of
an ordinary apothecary, and struggling against poverty.  His
treatise upon Air and Fire appeared in 1777.  In this remarkable
book he tells of his discovery of oxygen--"empyreal" or
"fire-air," as he calls it--which he seems to have made
independently and without ever having heard of the previous
discovery by Priestley.  In this book, also, he shows that air is
composed chiefly of oxygen and nitrogen gas.

Early in his experimental career Scheele undertook the solution
of the composition of black oxide of manganese, a substance that
had long puzzled the chemists.  He not only succeeded in this,
but incidentally in the course of this series of experiments he
discovered oxygen, baryta, and chlorine, the last of far greater
importance, at least commercially, than the real object of his
search.  In speaking of the experiment in which the discovery was
made he says:

"When marine (hydrochloric) acid stood over manganese in the cold
it acquired a dark reddish-brown color. As manganese does not
give any colorless solution without uniting with phlogiston
[probably meaning hydrogen], it follows that marine acid can
dissolve it without this principle. But such a solution has a
blue or red color.  The color is here more brown than red, the
reason being that the very finest portions of the manganese,
which do not sink so easily, swim in the red solution; for
without these fine particles the solution is red, and red mixed
with black is brown. The manganese has here attached itself so
loosely to acidum salis that the water can precipitate it, and
this precipitate behaves like ordinary manganese.  When, now, the
mixture of manganese and spiritus salis was set to digest, there
arose an effervescence and smell of aqua regis."[6]

The "effervescence" he refers to was chlorine, which he proceeded
to confine in a suitable vessel and examine more fully.  He
described it as having a "quite characteristically suffocating
smell," which was very offensive. He very soon noted the
decolorizing or bleaching effects of this now product, finding
that it decolorized flowers, vegetables, and many other
substances.

Commercially this discovery of chlorine was of enormous
importance, and the practical application of this new chemical in
bleaching cloth soon supplanted the, old process of
crofting--that is, bleaching by spreading the cloth upon the
grass. But although Scheele first pointed out the bleaching
quality of his newly discovered gas, it was the French savant,
Berthollet, who, acting upon Scheele's discovery that the new gas
would decolorize vegetables and flowers, was led to suspect that
this property might be turned to account in destroying the color
of cloth. In 1785 he read a paper before the Academy of Sciences
of Paris, in which he showed that bleaching by chlorine was
entirely satisfactory, the color but not the substance of the
cloth being affected. He had experimented previously and found
that the chlorine gas was soluble in water and could thus be made
practically available for bleaching purposes.  In 1786 James Watt
examined specimens of the bleached cloth made by Berthollet, and
upon his return to England first instituted the process of
practical bleaching. His process, however, was not entirely
satisfactory, and, after undergoing various modifications and
improvements, it was finally made thoroughly practicable by Mr.
Tennant, who hit upon a compound of chlorine and lime--the
chloride of lime--which was a comparatively cheap chemical
product, and answered the purpose better even than chlorine
itself.

To appreciate how momentous this discovery was to cloth
manufacturers, it should be remembered that the old process of
bleaching consumed an entire summer for the whitening of a single
piece of linen; the new process reduced the period to a few
hours.  To be sure, lime had been used with fair success previous
to Tennant's discovery, but successful and practical bleaching by
a solution of chloride of lime was first made possible by him and
through Scheele's discovery of chlorine.

Until the time of Scheele the great subject of organic chemistry
had remained practically unexplored, but under the touch of his
marvellous inventive genius new methods of isolating and studying
animal and vegetable products were introduced, and a large number
of acids and other organic compounds prepared that had been
hitherto unknown.  His explanations of chemical phenomena were
based on the phlogiston theory, in which, like Priestley, he
always, believed.  Although in error in this respect, he was,
nevertheless, able to make his discoveries with extremely
accurate interpretations. A brief epitome of the list of some of
his more important discoveries conveys some idea, of his
fertility of mind as well as his industry.  In 1780 he discovered
lactic acid,[7] and showed that it was the substance that caused
the acidity of sour milk; and in the same year he discovered
mucic acid. Next followed the discovery of tungstic acid, and in
1783 he added to his list of useful discoveries that of
glycerine. Then in rapid succession came his announcements of the
new vegetable products citric, malic, oxalic, and gallic acids.
Scheele not only made the discoveries, but told the world how he
had made them--how any chemist might have made them if he
chose--for he never considered that he had really discovered any
substance until he had made it, decomposed it, and made it again.

His experiments on Prussian blue are most interesting, not only
because of the enormous amount of work involved and the skill he
displayed in his experiments, but because all the time the
chemist was handling, smelling, and even tasting a compound of
one of the most deadly poisons, ignorant of the fact that the
substance was a dangerous one to handle. His escape from injury
seems almost miraculous; for his experiments, which were most
elaborate, extended over a considerable period of time, during
which he seems to have handled this chemical with impunity.

While only forty years of age and just at the zenith of his fame,
Scheele was stricken by a fatal illness, probably induced by his
ceaseless labor and exposure.  It is gratifying to know, however,
that during the last eight or nine years of his life he had been
less bound down by pecuniary difficulties than before, as Bergman
had obtained for him an annual grant from the Academy.  But it
was characteristic of the man that, while devoting one-sixth of
the amount of this grant to his personal wants, the remaining
five-sixths was devoted to the expense of his experiments.


LAVOISIER AND THE FOUNDATION OF MODERN CHEMISTRY

The time was ripe for formulating the correct theory of chemical
composition: it needed but the master hand to mould the materials
into the proper shape. The discoveries in chemistry during the
eighteenth century had been far-reaching and revolutionary in
character.  A brief review of these discoveries shows how
completely they had subverted the old ideas of chemical elements
and chemical compounds.  Of the four substances earth, air, fire,
and water, for many centuries believed to be elementary bodies,
not one has stood the test of the eighteenth-century chemists.
Earth had long since ceased to be regarded as an element, and
water and air had suffered the same fate in this century.  And
now at last fire itself, the last of the four "elements" and the
keystone to the phlogiston arch, was shown to be nothing more
than one of the manifestations of the new element, oxygen, and
not "phlogiston" or any other intangible substance.

In this epoch of chemical discoveries England had produced such
mental giants and pioneers in science as Black, Priestley, and
Cavendish; Sweden had given the world Scheele and Bergman, whose
work, added to that of their English confreres, had laid the
broad base of chemistry as a science; but it was for France to
produce a man who gave the final touches to the broad but rough
workmanship of its foundation, and establish it as the science of
modern chemistry.  It was for Antoine Laurent Lavoisier
(1743-1794) to gather together, interpret correctly, rename, and
classify the wealth of facts that his immediate predecessors and
contemporaries had given to the world.

The attitude of the mother-countries towards these illustrious
sons is an interesting piece of history.  Sweden honored and
rewarded Scheele and Bergman for their efforts; England received
the intellectuality of Cavendish with less appreciation than the
Continent, and a fanatical mob drove Priestley out of the
country; while France, by sending Lavoisier to the guillotine,
demonstrated how dangerous it was, at that time at least, for an
intelligent Frenchman to serve his fellowman and his country
well.

"The revolution brought about by Lavoisier in science," says
Hoefer, "coincides by a singular act of destiny with another
revolution, much greater indeed, going on then in the political
and social world. Both happened on the same soil, at the same
epoch, among the same people; and both marked the commencement of
a new era in their respective spheres."[8]

Lavoisier was born in Paris, and being the son of an opulent
family, was educated under the instruction of the best teachers
of the day. With Lacaille he studied mathematics and astronomy;
with Jussieu, botany; and, finally, chemistry under Rouelle.  His
first work of importance was a paper on the practical
illumination of the streets of Paris, for which a prize had been
offered by M. de Sartine, the chief of police. This prize was not
awarded to Lavoisier, but his suggestions were of such importance
that the king directed that a gold medal be bestowed upon the
young author at the public sitting of the Academy in April, 1776.
Two years later, at the age of thirty-five, Lavoisier was
admitted a member of the Academy.

In this same year he began to devote himself almost exclusively
to chemical inquiries, and established a laboratory in his home,
fitted with all manner of costly apparatus and chemicals. Here he
was in constant communication with the great men of science of
Paris, to all of whom his doors were thrown open. One of his
first undertakings in this laboratory was to demonstrate that
water could not be converted into earth by repeated
distillations, as was generally advocated; and to show also that
there was no foundation to the existing belief that it was
possible to convert water into a gas so "elastic" as to pass
through the pores of a vessel. He demonstrated the fallaciousness
of both these theories in 1768-1769 by elaborate experiments, a
single investigation of this series occupying one hundred and one
days.

In 1771 he gave the first blow to the phlogiston theory by his
experiments on the calcination of metals. It will be recalled
that one basis for the belief in phlogiston was the fact that
when a metal was calcined it was converted into an ash, giving up
its "phlogiston" in the process. To restore the metal, it was
necessary to add some substance such as wheat or charcoal to the
ash.  Lavoisier, in examining this process of restoration, found
that there was always evolved a great quantity of "air," which he
supposed to be "fixed air" or carbonic acid--the same that
escapes in effervescence of alkalies and calcareous earths, and
in the fermentation of liquors. He then examined the process of
calcination, whereby the phlogiston of the metal was supposed to
have been drawn off. But far from finding that phlogiston or any
other substance had been driven off, he found that something had
been taken on: that the metal "absorbed air," and that the
increased weight of the metal corresponded to the amount of air
"absorbed." Meanwhile he was within grasp of two great
discoveries, that of oxygen and of the composition of the air,
which Priestley made some two years later.

The next important inquiry of this great Frenchman was as to the
composition of diamonds.  With the great lens of Tschirnhausen
belonging to the Academy he succeeded in burning up several
diamonds, regardless of expense, which, thanks to his
inheritance, he could ignore. In this process he found that a gas
was given off which precipitated lime from water, and proved to
be carbonic acid.  Observing this, and experimenting with other
substances known to give off carbonic acid in the same manner, he
was evidently impressed with the now well-known fact that diamond
and charcoal are chemically the same. But if he did really
believe it, he was cautious in expressing his belief fully.  "We
should never have expected," he says, "to find any relation
between charcoal and diamond, and it would be unreasonable to
push this analogy too far; it only exists because both substances
seem to be properly ranged in the class of combustible bodies,
and because they are of all these bodies the most fixed when kept
from contact with air."

As we have seen, Priestley, in 1774, had discovered oxygen, or
"dephlogisticated air."  Four years later Lavoisier first
advanced his theory that this element discovered by Priestley was
the universal acidifying or oxygenating principle, which, when
combined with charcoal or carbon, formed carbonic acid; when
combined with sulphur, formed sulphuric (or vitriolic) acid; with
nitrogen, formed nitric acid, etc., and when combined with the
metals formed oxides, or calcides. Furthermore, he postulated the
theory that combustion was not due to any such illusive thing as
"phlogiston," since this did not exist, and it seemed to him that
the phenomena of combustion heretofore attributed to phlogiston
could be explained by the action of the new element oxygen and
heat. This was the final blow to the phlogiston theory, which,
although it had been tottering for some time, had not been
completely overthrown.

In 1787 Lavoisier, in conjunction with Guyon de Morveau,
Berthollet, and Fourcroy, introduced the reform in chemical
nomenclature which until then had remained practically unchanged
since alchemical days. Such expressions as "dephlogisticated" and
"phlogisticated" would obviously have little meaning to a
generation who were no longer to believe in the existence of
phlogiston.  It was appropriate that a revolution in chemical
thought should be accompanied by a corresponding revolution in
chemical names, and to Lavoisier belongs chiefly the credit of
bringing about this revolution. In his Elements of Chemistry he
made use of this new nomenclature, and it seemed so clearly an
improvement over the old that the scientific world hastened to
adopt it.  In this connection Lavoisier says: "We have,
therefore, laid aside the expression metallic calx altogether,
and have substituted in its place the word oxide.  By this it may
be seen that the language we have adopted is both copious and
expressive. The first or lowest degree of oxygenation in bodies
converts them into oxides; a second degree of additional
oxygenation constitutes the class of acids of which the specific
names drawn from their particular bases terminate in ous, as in
the nitrous and the sulphurous acids. The third degree of
oxygenation changes these into the species of acids distinguished
by the termination in ic, as the nitric and sulphuric acids; and,
lastly, we can express a fourth or higher degree of oxygenation
by adding the word oxygenated to the name of the acid, as has
already been done with oxygenated muriatic acid."[9]

This new work when given to the world was not merely an
epoch-making book; it was revolutionary.  It not only discarded
phlogiston altogether, but set forth that metals are simple
elements, not compounds of "earth" and "phlogiston."  It upheld
Cavendish's demonstration that water itself, like air, is a
compound of oxygen with another element.  In short, it was
scientific chemistry, in the modern acceptance of the term.

Lavoisier's observations on combustion are at once important and
interesting: "Combustion," he says, ". . . is the decomposition
of oxygen produced by a combustible body.  The oxygen which forms
the base of this gas is absorbed by and enters into combination
with the burning body, while the caloric and light are set free. 
Every combustion necessarily supposes oxygenation; whereas, on
the contrary, every oxygenation does not necessarily imply
concomitant combustion; because combustion properly so called
cannot take place without disengagement of caloric and light.
Before combustion can take place, it is necessary that the base
of oxygen gas should have greater affinity to the combustible
body than it has to caloric; and this elective attraction, to use
Bergman's expression, can only take place at a certain degree of
temperature which is different for each combustible substance;
hence the necessity of giving the first motion or beginning to
every combustion by the approach of a heated body. This necessity
of heating any body we mean to burn depends upon certain
considerations which have not hitherto been attended to by any
natural philosopher, for which reason I shall enlarge a little
upon the subject in this place:

"Nature is at present in a state of equilibrium, which cannot
have been attained until all the spontaneous combustions or
oxygenations possible in an ordinary degree of temperature had
taken place.... To illustrate this abstract view of the matter by
example: Let us suppose the usual temperature of the earth a
little changed, and it is raised only to the degree of boiling
water; it is evident that in this case phosphorus, which is
combustible in a considerably lower degree of temperature, would
no longer exist in nature in its pure and simple state, but would
always be procured in its acid or oxygenated state, and its
radical would become one of the substances unknown to chemistry.
By gradually increasing the temperature of the earth, the same
circumstance would successively happen to all the bodies capable
of combustion; and, at the last, every possible combustion having
taken place, there would no longer exist any combustible body
whatever, and every substance susceptible of the operation would
be oxygenated and consequently incombustible.

"There cannot, therefore, exist, as far as relates to us, any
combustible body but such as are non-combustible at the ordinary
temperature of the earth, or, what is the same thing in other
words, that it is essential to the nature of every combustible
body not to possess the property of combustion unless heated, or
raised to a degree of temperature at which its combustion
naturally takes place. When this degree is once produced,
combustion commences, and the caloric which is disengaged by the
decomposition of the oxygen gas keeps up the temperature which is
necessary for continuing combustion. When this is not the
case--that is, when the disengaged caloric is not sufficient for
keeping up the necessary temperature--the combustion ceases. This
circumstance is expressed in the common language by saying that a
body burns ill or with difficulty."[10]


It needed the genius of such a man as Lavoisier to complete the
refutation of the false but firmly grounded phlogiston theory,
and against such a book as his Elements of Chemistry the feeble
weapons of the supporters of the phlogiston theory were hurled in
vain.

But while chemists, as a class, had become converts to the new
chemistry before the end of the century, one man, Dr. Priestley,
whose work had done so much to found it, remained unconverted. 
In this, as in all his life-work, he showed himself to be a most
remarkable man. Davy said of him, a generation later, that no
other person ever discovered so many new and curious substances
as he; yet to the last he was only an amateur in science, his
profession, as we know, being the ministry. There is hardly
another case in history of a man not a specialist in science
accomplishing so much in original research as did this chemist,
physiologist, electrician; the mathematician, logician, and
moralist; the theologian, mental philosopher, and political
economist. He took all knowledge for his field; but how he found
time for his numberless researches and multifarious writings,
along with his every-day duties, must ever remain a mystery to
ordinary mortals.

That this marvellously receptive, flexible mind should have
refused acceptance to the clearly logical doctrines of the new
chemistry seems equally inexplicable.  But so it was.  To the
very last, after all his friends had capitulated, Priestley kept
up the fight. From America he sent out his last defy to the
enemy, in 1800, in a brochure entitled "The Doctrine of
Phlogiston Upheld," etc.  In the mind of its author it was little
less than a paean of victory; but all the world beside knew that
it was the swan-song of the doctrine of phlogiston. Despite the
defiance of this single warrior the battle was really lost and
won, and as the century closed "antiphlogistic" chemistry had
practical possession of the field.



III. CHEMISTRY SINCE THE TIME OF DALTON

JOHN DALTON AND THE ATOMIC THEORY

Small beginnings as have great endings--sometimes.  As a case in
point, note what came of the small, original effort of a
self-trained back-country Quaker youth named John Dalton, who
along towards the close of the eighteenth century became
interested in the weather, and was led to construct and use a
crude water-gauge to test the amount of the rainfall. The simple
experiments thus inaugurated led to no fewer than two hundred
thousand recorded observations regarding the weather, which
formed the basis for some of the most epochal discoveries in
meteorology, as we have seen.  But this was only a beginning. The
simple rain-gauge pointed the way to the most important
generalization of the nineteenth century in a field of science
with which, to the casual observer, it might seem to have no
alliance whatever.  The wonderful theory of atoms, on which the
whole gigantic structure of modern chemistry is founded, was the
logical outgrowth, in the mind of John Dalton, of those early
studies in meteorology.

The way it happened was this:  From studying the rainfall, Dalton
turned naturally to the complementary process of evaporation. He
was soon led to believe that vapor exists, in the atmosphere as
an independent gas.  But since two bodies cannot occupy the same
space at the same time, this implies that the various atmospheric
gases are really composed of discrete particles. These ultimate
particles are so small that we cannot see them--cannot, indeed,
more than vaguely imagine them--yet each particle of vapor, for
example, is just as much a portion of water as if it were a drop
out of the ocean, or, for that matter, the ocean itself.  But,
again, water is a compound substance, for it may be separated, as
Cavendish has shown, into the two elementary substances hydrogen
and oxygen.  Hence the atom of water must be composed of two
lesser atoms joined together. Imagine an atom of hydrogen and one
of oxygen.  Unite them, and we have an atom of water; sever them,
and the water no longer exists; but whether united or separate
the atoms of hydrogen and of oxygen remain hydrogen and oxygen
and nothing else.  Differently mixed together or united, atoms
produce different gross substances; but the elementary atoms
never change their chemical nature--their distinct personality.

It was about the year 1803 that Dalton first gained a full grasp
of the conception of the chemical atom.  At once he saw that the
hypothesis, if true, furnished a marvellous key to secrets of
matter hitherto insoluble--questions relating to the relative
proportions of the atoms themselves. It is known, for example,
that a certain bulk of hydrogen gas unites with a certain bulk of
oxygen gas to form water. If it be true that this combination
consists essentially of the union of atoms one with another (each
single atom of hydrogen united to a single atom of oxygen), then
the relative weights of the original masses of hydrogen and of
oxygen must be also the relative weights of each of their
respective atoms. If one pound of hydrogen unites with five and
one-half pounds of oxygen (as, according to Dalton's experiments,
it did), then the weight of the oxygen atom must be five and
one-half times that of the hydrogen atom. Other compounds may
plainly be tested in the same way. Dalton made numerous tests
before he published his theory. He found that hydrogen enters
into compounds in smaller proportions than any other element
known to him, and so, for convenience, determined to take the
weight of the hydrogen atom as unity.  The atomic weight of
oxygen then becomes (as given in Dalton's first table of 1803)
5.5; that of water (hydrogen plus oxygen) being of course 6.5.
The atomic weights of about a score of substances are given in
Dalton's first paper, which was read before the Literary and
Philosophical Society of Manchester, October 21, 1803.  I wonder
if Dalton himself, great and acute intellect though he had,
suspected, when he read that paper, that he was inaugurating one
of the most fertile movements ever entered on in the whole
history of science?

Be that as it may, it is certain enough that Dalton's
contemporaries were at first little impressed with the novel
atomic theory. Just at this time, as it chanced, a dispute was
waging in the field of chemistry regarding a matter of empirical
fact which must necessarily be settled before such a theory as
that of Dalton could even hope for a bearing.  This was the
question whether or not chemical elements unite with one another
always in definite proportions. Berthollet, the great co-worker
with Lavoisier, and now the most authoritative of living
chemists, contended that substances combine in almost
indefinitely graded proportions between fixed extremes. He held
that solution is really a form of chemical combination--a
position which, if accepted, left no room for argument.

But this contention of the master was most actively disputed, in
particular by Louis Joseph Proust, and all chemists of repute
were obliged to take sides with one or the other. For a time the
authority of Berthollet held out against the facts, but at last
accumulated evidence told for Proust and his followers, and
towards the close of the first decade of our century it came to
be generally conceded that chemical elements combine with one
another in fixed and definite proportions.

More than that.  As the analysts were led to weigh carefully the
quantities of combining elements, it was observed that the
proportions are not only definite, but that they bear a very
curious relation to one another. If element A combines with two
different proportions of element B to form two compounds, it
appears that the weight of the larger quantity of B is an exact
multiple of that of the smaller quantity. This curious relation
was noticed by Dr. Wollaston, one of the most accurate of
observers, and a little later it was confirmed by Johan Jakob
Berzelius, the great Swedish chemist, who was to be a dominating
influence in the chemical world for a generation to come.  But
this combination of elements in numerical proportions was exactly
what Dalton had noticed as early as 1802, and what bad led him
directly to the atomic weights. So the confirmation of this
essential point by chemists of such authority gave the strongest
confirmation to the atomic theory.

During these same years the rising authority of the French
chemical world, Joseph Louis Gay-Lussac, was conducting
experiments with gases, which he had undertaken at first in
conjunction with Humboldt, but which later on were conducted
independently. In 1809, the next year after the publication of
the first volume of Dalton's New System of Chemical Philosophy,
Gay-Lussac published the results of his observations, and among
other things brought out the remarkable fact that gases, under
the same conditions as to temperature and pressure, combine
always in definite numerical proportions as to volume. Exactly
two volumes of hydrogen, for example, combine with one volume of
oxygen to form water.  Moreover, the resulting compound gas
always bears a simple relation to the combining volumes. In the
case just cited, the union of two volumes of hydrogen and one of
oxygen results in precisely two volumes of water vapor.

Naturally enough, the champions of the atomic theory seized upon
these observations of Gay-Lussac as lending strong support to
their hypothesis--all of them, that is, but the curiously
self-reliant and self-sufficient author of the atomic theory
himself, who declined to accept the observations of the French
chemist as valid. Yet the observations of Gay-Lussac were
correct, as countless chemists since then have demonstrated anew,
and his theory of combination by volumes became one of the
foundation-stones of the atomic theory, despite the opposition of
the author of that theory.

The true explanation of Gay-Lussac's law of combination by
volumes was thought out almost immediately by an Italian savant,
Amadeo, Avogadro, and expressed in terms of the atomic theory.
The fact must be, said Avogadro, that under similar physical
conditions every form of gas contains exactly the same number of
ultimate particles in a given volume.  Each of these ultimate
physical particles may be composed of two or more atoms (as in
the case of water vapor), but such a compound atom conducts
itself as if it were a simple and indivisible atom, as regards
the amount of space that separates it from its fellows under
given conditions of pressure and temperature. The compound atom,
composed of two or more elementary atoms, Avogadro proposed to
distinguish, for purposes of convenience, by the name molecule. 
It is to the molecule, considered as the unit of physical
structure, that Avogadro's law applies.

This vastly important distinction between atoms and molecules,
implied in the law just expressed, was published in 1811. Four
years later, the famous French physicist Ampere outlined a
similar theory, and utilized the law in his mathematical
calculations. And with that the law of Avogadro dropped out of
sight for a full generation.  Little suspecting that it was the
very key to the inner mysteries of the atoms for which they were
seeking, the chemists of the time cast it aside, and let it fade
from the memory of their science.

This, however, was not strange, for of course the law of Avogadro
is based on the atomic theory, and in 1811 the atomic theory was
itself still being weighed in the balance. The law of multiple
proportions found general acceptance as an empirical fact; but
many of the leading lights of chemistry still looked askance at
Dalton's explanation of this law. Thus Wollaston, though from the
first he inclined to acceptance of the Daltonian view, cautiously
suggested that it would be well to use the non-committal word
"equivalent" instead of "atom"; and Davy, for a similar reason,
in his book of 1812, speaks only of "proportions," binding
himself to no theory as to what might be the nature of these
proportions.

At least two great chemists of the time, however, adopted the
atomic view with less reservation.  One of these was Thomas
Thomson, professor at Edinburgh, who, in 1807, had given an
outline of Dalton's theory in a widely circulated book, which
first brought the theory to the general attention of the chemical
world. The other and even more noted advocate of the atomic
theory was Johan Jakob Berzelius.  This great Swedish chemist at
once set to work to put the atomic theory to such tests as might
be applied in the laboratory.  He was an analyst of the utmost
skill, and for years be devoted himself to the determination of
the combining weights, "equivalents" or "proportions," of the
different elements. These determinations, in so far as they were
accurately made, were simple expressions of empirical facts,
independent of any theory; but gradually it became more and more
plain that these facts all harmonize with the atomic theory of
Dalton.  So by common consent the proportionate combining weights
of the elements came to be known as atomic weights--the name
Dalton had given them from the first--and the tangible conception
of the chemical atom as a body of definite constitution and
weight gained steadily in favor.

From the outset the idea had had the utmost tangibility in the
mind of Dalton.  He had all along represented the different atoms
by geometrical symbols--as a circle for oxygen, a circle
enclosing a dot for hydrogen, and the like--and had represented
compounds by placing these symbols of the elements in
juxtaposition. Berzelius proposed to improve upon this method by
substituting for the geometrical symbol the initial of the Latin
name of the element represented--O for oxygen, H for hydrogen,
and so on--a numerical coefficient to follow the letter as an
indication of the number of atoms present in any given compound.
This simple system soon gained general acceptance, and with
slight modifications it is still universally employed. Every
school-boy now is aware that H2O is the chemical way of
expressing the union of two atoms of hydrogen with one of oxygen
to form a molecule of water.  But such a formula would have had
no meaning for the wisest chemist before the day of Berzelius.

The universal fame of the great Swedish authority served to give
general currency to his symbols and atomic weights, and the new
point of view thus developed led presently to two important
discoveries which removed the last lingering doubts as to the
validity of the atomic theory. In 1819 two French physicists,
Dulong and Petit, while experimenting with heat, discovered that
the specific heats of solids (that is to say, the amount of heat
required to raise the temperature of a given mass to a given
degree) vary inversely as their atomic weights. In the same year
Eilhard Mitscherlich, a German investigator, observed that
compounds having the same number of atoms to the molecule are
disposed to form the same angles of crystallization--a property
which he called isomorphism.

Here, then, were two utterly novel and independent sets of
empirical facts which harmonize strangely with the supposition
that substances are composed of chemical atoms of a determinate
weight. This surely could not be coincidence--it tells of law.
And so as soon as the claims of Dulong and Petit and of
Mitscherlich had been substantiated by other observers, the laws
of the specific heat of atoms, and of isomorphism, took their
place as new levers of chemical science.  With the aid of these
new tools an impregnable breastwork of facts was soon piled about
the atomic theory. And John Dalton, the author of that theory,
plain, provincial Quaker, working on to the end in
semi-retirement, became known to all the world and for all time
as a master of masters.


HUMPHRY DAVY AND ELECTRO-CHEMISTRY

During those early years of the nineteenth century, when Dalton
was grinding away at chemical fact and theory in his obscure
Manchester laboratory, another Englishman held the attention of
the chemical world with a series of the most brilliant and widely
heralded researches.  This was Humphry Davy, a young man who had
conic to London in 1801, at the instance of Count Rumford, to
assume the chair of chemical philosophy in the Royal Institution,
which the famous American had just founded.

Here, under Davy's direction, the largest voltaic battery yet
constructed had been put in operation, and with its aid the
brilliant young experimenter was expected almost to perform
miracles. And indeed he scarcely disappointed the expectation,
for with the aid of his battery he transformed so familiar a
substance as common potash into a metal which was not only so
light that it floated on water, but possessed the seemingly
miraculous property of bursting into flames as soon as it came in
contact with that fire-quenching liquid. If this were not a
miracle, it had for the popular eye all the appearance of the
miraculous.

What Davy really had done was to decompose the potash, which
hitherto had been supposed to be elementary, liberating its
oxygen, and thus isolating its metallic base, which he named
potassium. The same thing was done with soda, and the closely
similar metal sodium was discovered--metals of a unique type,
possessed of a strange avidity for oxygen, and capable of seizing
on it even when it is bound up in the molecules of water.
Considered as mere curiosities, these discoveries were
interesting, but aside from that they were of great theoretical
importance, because they showed the compound nature of some
familiar chemicals that had been regarded as elements.  Several
other elementary earths met the same fate when subjected to the
electrical influence; the metals barium, calcium, and strontium
being thus discovered. Thereafter Davy always referred to the
supposed elementary substances (including oxygen, hydrogen, and
the rest) as "unde-compounded" bodies. These resist all present
efforts to decompose them, but how can one know what might not
happen were they subjected to an influence, perhaps some day to
be discovered, which exceeds the battery in power as the battery
exceeds the blowpipe?

Another and even more important theoretical result that flowed
from Davy's experiments during this first decade of the century
was the proof that no elementary substances other than hydrogen
and oxygen are produced when pure water is decomposed by the
electric current. It was early noticed by Davy and others that
when a strong current is passed through water, alkalies appear at
one pole of the battery and acids at the other, and this though
the water used were absolutely pure. This seemingly told of the
creation of elements--a transmutation but one step removed from
the creation of matter itself--under the influence of the new
"force."  It was one of Davy's greatest triumphs to prove, in the
series of experiments recorded in his famous Bakerian lecture of
1806, that the alleged creation of elements did not take place,
the substances found at the poles of the battery having been
dissolved from the walls of the vessels in which the water
experimented upon had been placed. Thus the same implement which
had served to give a certain philosophical warrant to the fading
dreams of alchemy banished those dreams peremptorily from the
domain of present science.

"As early as 1800," writes Davy, "I had found that when separate
portions of distilled water, filling two glass tubes, connected
by moist bladders, or any moist animal or vegetable substances,
were submitted to the electrical action of the pile of Volta by
means of gold wires, a nitro-muriatic solution of gold appeared
in the tube containing the positive wire, or the wire
transmitting the electricity, and a solution of soda in the
opposite tube; but I soon ascertained that the muriatic acid owed
its existence to the animal or vegetable matters employed; for
when the same fibres of cotton were made use of in successive
experiments, and washed after every process in a weak solution of
nitric acid, the water in the apparatus containing them, though
acted on for a great length of time with a very strong power, at
last produced no effects upon nitrate of silver.

"In cases when I had procured much soda, the glass at its point
of contact with the wire seemed considerably corroded; and I was
confirmed in my idea of referring the production of the alkali
principally to this source, by finding that no fixed saline
matter could be obtained by electrifying distilled water in a
single agate cup from two points of platina with the Voltaic
battery.

"Mr. Sylvester, however, in a paper published in Mr. Nicholson's
journal for last August, states that though no fixed alkali or
muriatic acid appears when a single vessel is employed, yet that
they are both formed when two vessels are used. And to do away
with all objections with regard to vegetable substances or glass,
he conducted his process in a vessel made of baked tobacco-pipe
clay inserted in a crucible of platina. I have no doubt of the
correctness of his results; but the conclusion appears
objectionable.  He conceives, that he obtained fixed alkali,
because the fluid after being heated and evaporated left a matter
that tinged turmeric brown, which would have happened had it been
lime, a substance that exists in considerable quantities in all
pipe-clay; and even allowing the presence of fixed alkali, the
materials employed for the manufacture of tobacco-pipes are not
at all such as to exclude the combinations of this substance.

"I resumed the inquiry; I procured small cylindrical cups of
agate of the capacity of about one-quarter of a cubic inch each.
They were boiled for some hours in distilled water, and a piece
of very white and transparent amianthus that had been treated in
the same way was made then to connect together; they were filled
with distilled water and exposed by means of two platina wires to
a current of electricity, from one hundred and fifty pairs of
plates of copper and zinc four inches square, made active by
means of solution of alum. After forty-eight hours the process
was examined: Paper tinged with litmus plunged into the tube
containing the transmitting or positive wire was immediately
strongly reddened. Paper colored by turmeric introduced into the
other tube had its color much deepened; the acid matter gave a
very slight degree of turgidness to solution of nitrate of soda.
The fluid that affected turmeric retained this property after
being strongly boiled; and it appeared more vivid as the quantity
became reduced by evaporation; carbonate of ammonia was mixed
with it, and the whole dried and exposed to a strong heat; a
minute quantity of white matter remained, which, as far as my
examinations could go, had the properties of carbonate of soda. I
compared it with similar minute portions of the pure carbonates
of potash, and similar minute portions of the pure carbonates of
potash and soda.  It was not so deliquescent as the former of
these bodies, and it formed a salt with nitric acid, which, like
nitrate of soda, soon attracted moisture from a damp atmosphere
and became fluid.

"This result was unexpected, but it was far from convincing me
that the substances which were obtained were generated. In a
similar process with glass tubes, carried on under exactly the
same circumstances and for the same time, I obtained a quantity
of alkali which must have been more than twenty times greater,
but no traces of muriatic acid. There was much probability that
the agate contained some minute portion of saline matter, not
easily detected by chemical analysis, either in combination or
intimate cohesion in its pores. To determine this, I repeated
this a second, a third, and a fourth time.  In the second
experiment turbidness was still produced by a solution of nitrate
of silver in the tube containing the acid, but it was less
distinct; in the third process it was barely perceptible; and in
the fourth process the two fluids remained perfectly clear after
the mixture. The quantity of alkaline matter diminished in every
operation; and in the last process, though the battery had been
kept in great activity for three days, the fluid possessed, in a
very slight degree, only the power of acting on paper tinged with
turmeric; but its alkaline property was very sensible to litmus
paper slightly reddened, which is a much more delicate test; and
after evaporation and the process by carbonate of ammonia, a
barely perceptible quantity of fixed alkali was still left. The
acid matter in the other tube was abundant; its taste was sour;
it smelled like water over which large quantities of nitrous gas
have been long kept; it did not effect solution of muriate of
barytes; and a drop of it placed upon a polished plate of silver
left, after evaporation, a black stain, precisely similar to that
produced by extremely diluted nitrous acid.

"After these results I could no longer doubt that some saline
matter existing in the agate tubes had been the source of the
acid matter capable of precipitating nitrate of silver and much
of the alkali. Four additional repetitions of the process,
however, convinced me that there was likewise some other cause
for the presence of this last substance; for it continued to
appear to the last in quantities sufficiently distinguishable,
and apparently equal in every case. I had used every precaution,
I had included the tube in glass vessels out of the reach of the
circulating air; all the acting materials had been repeatedly
washed with distilled water; and no part of them in contact with
the fluid had been touched by the fingers.

"The only substance that I could now conceive as furnishing the
fixed alkali was the water itself.  This water appeared pure by
the tests of nitrate of silver and muriate of barytes; but potash
of soda, as is well known, rises in small quantities in rapid
distillation; and the New River water which I made use of
contains animal and vegetable impurities, which it was easy to
conceive might furnish neutral salts capable of being carried
over in vivid ebullition."[1] Further experiment proved the
correctness of this inference, and the last doubt as to the
origin of the puzzling chemical was dispelled.

Though the presence of the alkalies and acids in the water was
explained, however, their respective migrations to the negative
and positive poles of the battery remained to be accounted for.
Davy's classical explanation assumed that different elements
differ among themselves as to their electrical properties, some
being positively, others negatively, electrified.  Electricity
and "chemical affinity," he said, apparently are manifestations
of the same force, acting in the one case on masses, in the other
on particles. Electro-positive particles unite with
electro-negative particles to form chemical compounds, in virtue
of the familiar principle that opposite electricities attract one
another. When compounds are decomposed by the battery, this
mutual attraction is overcome by the stronger attraction of the
poles of the battery itself.

This theory of binary composition of all chemical compounds,
through the union of electro-positive and electro-negative atoms
or molecules, was extended by Berzelius, and made the basis of
his famous system of theoretical chemistry.  This theory held
that all inorganic compounds, however complex their composition,
are essentially composed of such binary combinations. For many
years this view enjoyed almost undisputed sway. It received what
seemed strong confirmation when Faraday showed the definite
connection between the amount of electricity employed and the
amount of decomposition produced in the so-called electrolyte.
But its claims were really much too comprehensive, as subsequent
discoveries proved.


ORGANIC CHEMISTRY AND THE IDEA OF THE MOLECULE

When Berzelius first promulgated his binary theory he was careful
to restrict its unmodified application to the compounds of the
inorganic world.  At that time, and for a long time thereafter,
it was supposed that substances of organic nature had some
properties that kept them aloof from the domain of inorganic
chemistry. It was little doubted that a so-called "vital force"
operated here, replacing or modifying the action of ordinary
"chemical affinity." It was, indeed, admitted that organic
compounds are composed of familiar elements--chiefly carbon,
oxygen, hydrogen, and nitrogen; but these elements were supposed
to be united in ways that could not be imitated in the domain of
the non-living. It was regarded almost as an axiom of chemistry
that no organic compound whatever could be put together from its
elements--synthesized--in the laboratory. To effect the synthesis
of even the simplest organic compound, it was thought that the
"vital force" must be in operation.

Therefore a veritable sensation was created in the chemical world
when, in the year 1828, it was announced that the young German
chemist, Friedrich Wohler, formerly pupil of Berzelius, and
already known as a coming master, had actually synthesized the
well-known organic product urea in his laboratory at Sacrow.  The
"exception which proves the rule" is something never heard of in
the domain of logical science.  Natural law knows no exceptions. 
So the synthesis of a single organic compound sufficed at a blow
to break down the chemical barrier which the imagination of the
fathers of the science had erected between animate and inanimate
nature. Thenceforth the philosophical chemist would regard the
plant and animal organisms as chemical laboratories in which
conditions are peculiarly favorable for building up complex
compounds of a few familiar elements, under the operation of
universal chemical laws.  The chimera "vital force" could no
longer gain recognition in the domain of chemistry.

Now a wave of interest in organic chemistry swept over the
chemical world, and soon the study of carbon compounds became as
much the fashion as electrochemistry had been in the, preceding
generation.

Foremost among the workers who rendered this epoch of organic
chemistry memorable were Justus Liebig in Germany and Jean
Baptiste Andre Dumas in France, and their respective pupils,
Charles Frederic Gerhardt and Augustus Laurent.  Wohler, too,
must be named in the same breath, as also must Louis Pasteur,
who, though somewhat younger than the others, came upon the scene
in time to take chief part in the most important of the
controversies that grew out of their labors.

Several years earlier than this the way had been paved for the
study of organic substances by Gay-Lussac's discovery, made in
1815, that a certain compound of carbon and nitrogen, which he
named cyanogen, has a peculiar degree of stability which enables
it to retain its identity and enter into chemical relations after
the manner of a simple body. A year later Ampere discovered that
nitrogen and hydrogen, when combined in certain proportions to
form what he called ammonium, have the same property. Berzelius
had seized upon this discovery of the compound radical, as it was
called, because it seemed to lend aid to his dualistic theory. He
conceived the idea that all organic compounds are binary unions
of various compound radicals with an atom of oxygen, announcing
this theory in 1818. Ten years later, Liebig and Wohler undertook
a joint investigation which resulted in proving that compound
radicals are indeed very abundant among organic substances.  Thus
the theory of Berzelius seemed to be substantiated, and organic
chemistry came to be defined as the chemistry of compound
radicals.

But even in the day of its seeming triumph the dualistic theory
was destined to receive a rude shock.  This came about through
the investigations of Dumas, who proved that in a certain organic
substance an atom of hydrogen may be removed and an atom of
chlorine substituted in its place without destroying the
integrity of the original compound--much as a child might
substitute one block for another in its play-house. Such a
substitution would be quite consistent with the dualistic theory,
were it not for the very essential fact that hydrogen is a
powerfully electro-positive element, while chlorine is as
strongly electro-negative. Hence the compound radical which
united successively with these two elements must itself be at one
time electro-positive, at another electro-negative--a seeming
inconsistency which threw the entire Berzelian theory into
disfavor.

In its place there was elaborated, chiefly through the efforts of
Laurent and Gerhardt, a conception of the molecule as a unitary
structure, built up through the aggregation of various atoms, in
accordance with "elective affinities" whose nature is not yet
understood A doctrine of "nuclei" and a doctrine of "types" of
molecular structure were much exploited, and, like the doctrine
of compound radicals, became useful as aids to memory and guides
for the analyst, indicating some of the plans of molecular
construction, though by no means penetrating the mysteries of
chemical affinity. They are classifications rather than
explanations of chemical unions.  But at least they served an
important purpose in giving definiteness to the idea of a
molecular structure built of atoms as the basis of all
substances. Now at last the word molecule came to have a distinct
meaning, as distinct from "atom," in the minds of the generality
of chemists, as it had had for Avogadro a third of a century
before. Avogadro's hypothesis that there are equal numbers of
these molecules in equal volumes of gases, under fixed
conditions, was revived by Gerhardt, and a little later, under
the championship of Cannizzaro, was exalted to the plane of a
fixed law. Thenceforth the conception of the molecule was to be
as dominant a thought in chemistry as the idea of the atom had
become in a previous epoch.


CHEMICAL AFFINITY

Of course the atom itself was in no sense displaced, but
Avogadro's law soon made it plain that the atom had often usurped
territory that did not really belong to it. In many cases the
chemists had supposed themselves dealing with atoms as units
where the true unit was the molecule. In the case of elementary
gases, such as hydrogen and oxygen, for example, the law of equal
numbers of molecules in equal spaces made it clear that the atoms
do not exist isolated, as had been supposed.  Since two volumes
of hydrogen unite with one volume of oxygen to form two volumes
of water vapor, the simplest mathematics show, in the light of
Avogadro's law, not only that each molecule of water must contain
two hydrogen atoms (a point previously in dispute), but that the
original molecules of hydrogen and oxygen must have been composed
in each case of two atoms---else how could one volume of oxygen
supply an atom for every molecule of two volumes of water?

What, then, does this imply?  Why, that the elementary atom has
an avidity for other atoms, a longing for companionship, an
"affinity"--call it what you will--which is bound to be satisfied
if other atoms are in the neighborhood.  Placed solely among
atoms of its own kind, the oxygen atom seizes on a fellow oxygen
atom, and in all their mad dancings these two mates cling
together--possibly revolving about each other in miniature
planetary orbits. Precisely the same thing occurs among the
hydrogen atoms. But now suppose the various pairs of oxygen atoms
come near other pairs of hydrogen atoms (under proper conditions
which need not detain us here), then each oxygen atom loses its
attachment for its fellow, and flings itself madly into the
circuit of one of the hydrogen couplets, and--presto!--there are
only two molecules for every three there were before, and free
oxygen and hydrogen have become water. The whole process, stated
in chemical phraseology, is summed up in the statement that under
the given conditions the oxygen atoms had a greater affinity for
the hydrogen atoms than for one another.

As chemists studied the actions of various kinds of atoms, in
regard to their unions with one another to form molecules, it
gradually dawned upon them that not all elements are satisfied
with the same number of companions. Some elements ask only one,
and refuse to take more; while others link themselves, when
occasion offers, with two, three, four, or more. Thus we saw that
oxygen forsook a single atom of its own kind and linked itself
with two atoms of hydrogen.  Clearly, then, the oxygen atom, like
a creature with two hands, is able to clutch two other atoms. 
But we have no proof that under any circumstances it could hold
more than two. Its affinities seem satisfied when it has two
bonds.  But, on the other hand, the atom of nitrogen is able to
hold three atoms of hydrogen, and does so in the molecule of
ammonium (NH3); while the carbon atom can hold four atoms of
hydrogen or two atoms of oxygen.

Evidently, then, one atom is not always equivalent to another
atom of a different kind in combining powers.  A recognition of
this fact by Frankland about 1852, and its further investigation
by others (notably A. Kekule and A. S. Couper), led to the
introduction of the word equivalent into chemical terminology in
a new sense, and in particular to an understanding of the
affinities or "valency" of different elements, which proved of
the most fundamental importance. Thus it was shown that, of the
four elements that enter most prominently into organic compounds,
hydrogen can link itself with only a single bond to any other
element--it has, so to speak, but a single hand with which to
grasp--while oxygen has capacity for two bonds, nitrogen for
three (possibly for five), and carbon for four. The words
monovalent, divalent, trivalent, tretrava-lent, etc., were coined
to express this most important fact, and the various elements
came to be known as monads, diads, triads, etc.  Just why
different elements should differ thus in valency no one as yet
knows; it is an empirical fact that they do.  And once the nature
of any element has been determined as regards its valency, a most
important insight into the possible behavior of that element has
been secured. Thus a consideration of the fact that hydrogen is
monovalent, while oxygen is divalent, makes it plain that we must
expect to find no more than three compounds of these two
elements--namely, H--O--(written HO by the chemist, and called
hydroxyl); H--O--H (H2O, or water), and H--O--O--H (H2O2, or
hydrogen peroxide). It will be observed that in the first of
these compounds the atom of oxygen stands, so to speak, with one
of its hands free, eagerly reaching out, therefore, for another
companion, and hence, in the language of chemistry, forming an
unstable compound. Again, in the third compound, though all hands
are clasped, yet one pair links oxygen with oxygen; and this also
must be an unstable union, since the avidity of an atom for its
own kind is relatively weak. Thus the well-known properties of
hydrogen peroxide are explained, its easy decomposition, and the
eagerness with which it seizes upon the elements of other
compounds.

But the molecule of water, on the other hand, has its atoms
arranged in a state of stable equilibrium, all their affinities
being satisfied.  Each hydrogen atom has satisfied its own
affinity by clutching the oxygen atom; and the oxygen atom has
both its bonds satisfied by clutching back at the two hydrogen
atoms. Therefore the trio, linked in this close bond, have no
tendency to reach out for any other companion, nor, indeed, any
power to hold another should it thrust itself upon them. They
form a "stable" compound, which under all ordinary circumstances
will retain its identity as a molecule of water, even though the
physical mass of which it is a part changes its condition from a
solid to a gas from ice to vapor.

But a consideration of this condition of stable equilibrium in
the molecule at once suggests a new question: How can an
aggregation of atoms, having all their affinities satisfied, take
any further part in chemical reactions? Seemingly such a
molecule, whatever its physical properties, must be chemically
inert, incapable of any atomic readjustments. And so in point of
fact it is, so long as its component atoms cling to one another
unremittingly.  But this, it appears, is precisely what the atoms
are little prone to do. It seems that they are fickle to the last
degree in their individual attachments, and are as prone to break
away from bondage as they are to enter into it.  Thus the oxygen
atom which has just flung itself into the circuit of two hydrogen
atoms, the next moment flings itself free again and seeks new
companions. It is for all the world like the incessant change of
partners in a rollicking dance.  This incessant dissolution and
reformation of molecules in a substance which as a whole remains
apparently unchanged was first fully appreciated by Ste.-Claire
Deville, and by him named dissociation.  It is a process which
goes on much more actively in some compounds than in others, and
very much more actively under some physical conditions (such as
increase of temperature) than under others.  But apparently no
substances at ordinary temperatures, and no temperature above the
absolute zero, are absolutely free from its disturbing influence.
Hence it is that molecules having all the valency of their atoms
fully satisfied do not lose their chemical activity--since each
atom is momentarily free in the exchange of partners, and may
seize upon different atoms from its former partners, if those it
prefers are at hand.

While, however, an appreciation of this ceaseless activity of the
atom is essential to a proper understanding of its chemical
efficiency, yet from another point of view the "saturated"
molecule--that is, the molecule whose atoms have their valency
all satisfied--may be thought of as a relatively fixed or stable
organism. Even though it may presently be torn down, it is for
the time being a completed structure; and a consideration of the
valency of its atoms gives the best clew that has hitherto been
obtainable as to the character of its architecture.  How
important this matter of architecture of the molecule--of space
relations of the atoms--may be was demonstrated as long ago as
1823, when Liebig and Wohler proved, to the utter bewilderment of
the chemical world, that two substances may have precisely the
same chemical constitution--the same number and kind of
atoms--and yet differ utterly in physical properties. The word
isomerism was coined by Berzelius to express this anomalous
condition of things, which seemed to negative the most
fundamental truths of chemistry.  Naming the condition by no
means explained it, but the fact was made clear that something
besides the mere number and kind of atoms is important in the
architecture of a molecule. It became certain that atoms are not
thrown together haphazard to build a molecule, any more than
bricks are thrown together at random to form a house.

How delicate may be the gradations of architectural design in
building a molecule was well illustrated about 1850, when Pasteur
discovered that some carbon compounds--as certain sugars--can
only be distinguished from one another, when in solution, by the
fact of their twisting or polarizing a ray of light to the left
or to the right, respectively. But no inkling of an explanation
of these strange variations of molecular structure came until the
discovery of the law of valency.  Then much of the mystery was
cleared away; for it was plain that since each atom in a molecule
can hold to itself only a fixed number of other atoms, complex
molecules must have their atoms linked in definite chains or
groups. And it is equally plain that where the atoms are
numerous, the exact plan of grouping may sometimes be susceptible
of change without doing violence to the law of valency. It is in
such cases that isomerism is observed to occur.

By paying constant heed to this matter of the affinities,
chemists are able to make diagrammatic pictures of the plan of
architecture of any molecule whose composition is known. In the
simple molecule of water (H2O), for example, the two hydrogen
atoms must have released each other before they could join the
oxygen, and the manner of linking must apparently be that
represented in the graphic formula H--O--H. With molecules
composed of a large number of atoms, such graphic representation
of the scheme of linking is of course increasingly difficult,
yet, with the affinities for a guide, it is always possible. Of
course no one supposes that such a formula, written in a single
plane, can possibly represent the true architecture of the
molecule: it is at best suggestive or diagrammatic rather than
pictorial. Nevertheless, it affords hints as to the structure of
the molecule such as the fathers of chemistry would not have
thought it possible ever to attain.


PERIODICITY OF ATOMIC WEIGHTS

These utterly novel studies of molecular architecture may seem at
first sight to take from the atom much of its former prestige as
the all-important personage of the chemical world. Since so much
depends upon the mere position of the atoms, it may appear that
comparatively little depends upon the nature of the atoms
themselves.  But such a view is incorrect, for on closer
consideration it will appear that at no time has the atom been
seen to renounce its peculiar personality. Within certain limits
the character of a molecule may be altered by changing the
positions of its atoms (just as different buildings may be
constructed of the same bricks), but these limits are sharply
defined, and it would be as impossible to exceed them as it would
be to build a stone building with bricks. From first to last the
brick remains a brick, whatever the style of architecture it
helps to construct; it never becomes a stone. And just as closely
does each atom retain its own peculiar properties, regardless of
its surroundings.

Thus, for example, the carbon atom may take part in the formation
at one time of a diamond, again of a piece of coal, and yet again
of a particle of sugar, of wood fibre, of animal tissue, or of a
gas in the atmosphere; but from first to last--from glass-cutting
gem to intangible gas--there is no demonstrable change whatever
in any single property of the atom itself. So far as we know, its
size, its weight, its capacity for vibration or rotation, and its
inherent affinities, remain absolutely unchanged throughout all
these varying fortunes of position and association. And the same
thing is true of every atom of all of the seventy-odd elementary
substances with which the modern chemist is acquainted. Every one
appears always to maintain its unique integrity, gaining nothing
and losing nothing.

All this being true, it would seem as if the position of the
Daltonian atom as a primordial bit of matter, indestructible and
non-transmutable, had been put to the test by the chemistry of
our century, and not found wanting. Since those early days of the
century when the electric battery performed its miracles and
seemingly reached its limitations in the hands of Davy, many new
elementary substances have been discovered, but no single element
has been displaced from its position as an undecomposable body.
Rather have the analyses of the chemist seemed to make it more
and more certain that all elementary atoms are in truth what John
Herschel called them, "manufactured articles"--primordial,
changeless, indestructible.

And yet, oddly enough, it has chanced that hand in hand with the
experiments leading to such a goal have gone other experiments
arid speculations of exactly the opposite tenor. In each
generation there have been chemists among the leaders of their
science who have refused to admit that the so-called elements are
really elements at all in any final sense, and who have sought
eagerly for proof which might warrant their scepticism. The first
bit of evidence tending to support this view was furnished by an
English physician, Dr. William Prout, who in 1815 called
attention to a curious relation to be observed between the atomic
weight of the various elements. Accepting the figures given by
the authorities of the time (notably Thomson and Berzelius), it
appeared that a strikingly large proportion of the atomic weights
were exact multiples of the weight of hydrogen, and that others
differed so slightly that errors of observation might explain the
discrepancy. Prout felt that it could not be accidental, and he
could think of no tenable explanation, unless it be that the
atoms of the various alleged elements are made up of different
fixed numbers of hydrogen atoms.  Could it be that the one true
element--the one primal matter--is hydrogen, and that all other
forms of matter are but compounds of this original substance?

Prout advanced this startling idea at first tentatively, in an
anonymous publication; but afterwards he espoused it openly and
urged its tenability.  Coming just after Davy's dissociation of
some supposed elements, the idea proved alluring, and for a time
gained such popularity that chemists were disposed to round out
the observed atomic weights of all elements into whole numbers.
But presently renewed determinations of the atomic weights seemed
to discountenance this practice, and Prout's alleged law fell
into disrepute.  It was revived, however, about 1840, by Dumas,
whose great authority secured it a respectful hearing, and whose
careful redetermination of the weight of carbon, making it
exactly twelve times that of hydrogen, aided the cause.

Subsequently Stas, the pupil of Dumas, undertook a long series of
determinations of atomic weights, with the expectation of
confirming the Proutian hypothesis.  But his results seemed to
disprove the hypothesis, for the atomic weights of many elements
differed from whole numbers by more, it was thought, than the
limits of error of the experiments. It was noteworthy, however,
that the confidence of Dumas was not shaken, though he was led to
modify the hypothesis, and, in accordance with previous
suggestions of Clark and of Marignac, to recognize as the
primordial element, not hydrogen itself, but an atom half the
weight, or even one-fourth the weight, of that of hydrogen, of
which primordial atom the hydrogen atom itself is compounded. But
even in this modified form the hypothesis found great opposition
from experimental observers.

In 1864, however, a novel relation between the weights of the
elements and their other characteristics was called to the
attention of chemists by Professor John A. R. Newlands, of
London, who had noticed that if the elements are arranged
serially in the numerical order of their atomic weights, there is
a curious recurrence of similar properties at intervals of eight
elements This so-called "law of octaves" attracted little
immediate attention, but the facts it connotes soon came under
the observation of other chemists, notably of Professors Gustav
Hinrichs in America, Dmitri Mendeleeff in Russia, and Lothar
Meyer in Germany.  Mendeleeff gave the discovery fullest
expression, explicating it in 1869, under the title of "the
periodic law."

Though this early exposition of what has since been admitted to
be a most important discovery was very fully outlined, the
generality of chemists gave it little heed till a decade or so
later, when three new elements, gallium, scandium, and germanium,
were discovered, which, on being analyzed, were quite
unexpectedly found to fit into three gaps which Mendeleeff had
left in his periodic scale. In effect the periodic law had
enabled Mendeleeff to predicate the existence of the new elements
years before they were discovered. Surely a system that leads to
such results is no mere vagary. So very soon the periodic law
took its place as one of the most important generalizations of
chemical science.

This law of periodicity was put forward as an expression of
observed relations independent of hypothesis; but of course the
theoretical bearings of these facts could not be overlooked. As
Professor J. H. Gladstone has said, it forces upon us "the
conviction that the elements are not separate bodies created
without reference to one another, but that they have been
originally fashioned, or have been built up, from one another,
according to some general plan."  It is but a short step from
that proposition to the Proutian hypothesis.


NEW WEAPONS--SPECTROSCOPE AND CAMERA

But the atomic weights are not alone in suggesting the compound
nature of the alleged elements.  Evidence of a totally different
kind has contributed to the same end, from a source that could
hardly have been imagined when the Proutian hypothesis, was
formulated, through the tradition of a novel weapon to the
armamentarium of the chemist--the spectroscope.  The perfection
of this instrument, in the hands of two German scientists, Gustav
Robert Kirchhoff and Robert Wilhelm Bunsen, came about through
the investigation, towards the middle of the century, of the
meaning of the dark lines which had been observed in the solar
spectrum by Fraunhofer as early as 1815, and by Wollaston a
decade earlier. It was suspected by Stokes and by Fox Talbot in
England, but first brought to demonstration by Kirchhoff and
Bunsen, that these lines, which were known to occupy definite
positions in the spectrum, are really indicative of particular
elementary substances. By means of the spectroscope, which is
essentially a magnifying lens attached to a prism of glass, it is
possible to locate the lines with great accuracy, and it was soon
shown that here was a new means of chemical analysis of the most
exquisite delicacy. It was found, for example, that the
spectroscope could detect the presence of a quantity of sodium so
infinitesimal as the one two-hundred-thousandth of a grain.  But
what was even more important, the spectroscope put no limit upon
the distance of location of the substance it tested, provided
only that sufficient light came from it. The experiments it
recorded might be performed in the sun, or in the most distant
stars or nebulae; indeed, one of the earliest feats of the
instrument was to wrench from the sun the secret of his chemical
constitution.

To render the utility of the spectroscope complete, however, it
was necessary to link with it another new chemical
agency--namely, photography.  This now familiar process is based
on the property of light to decompose certain unstable compounds
of silver, and thus alter their chemical composition. Davy and
Wedgwood barely escaped the discovery of the value of the
photographic method early in the nineteenth century. Their
successors quite overlooked it until about 1826, when Louis J. M.
Daguerre, the French chemist, took the matter in hand, and after
many years of experimentation brought it to relative perfection
in 1839, in which year the famous daguerreotype first brought the
matter to popular attention. In the same year Mr. Fox Talbot read
a paper on the subject before the Royal Society, and soon
afterwards the efforts of Herschel and numerous other natural
philosophers contributed to the advancement of the new method.

In 1843 Dr. John W. Draper, the famous English-American chemist
and physiologist, showed that by photography the Fraunhofer lines
in the solar spectrum might be mapped with absolute accuracy;
also proving that the silvered film revealed many lines invisible
to the unaided eye. The value of this method of observation was
recognized at once, and, as soon as the spectroscope was
perfected, the photographic method, in conjunction with its use,
became invaluable to the chemist. By this means comparisons of
spectra may be made with a degree of accuracy not otherwise
obtainable; and, in case of the stars, whole clusters of spectra
may be placed on record at a single observation.

As the examination of the sun and stars proceeded, chemists were
amazed or delighted, according to their various preconceptions,
to witness the proof that many familiar terrestrial elements are
to be found in the celestial bodies.  But what perhaps surprised
them most was to observe the enormous preponderance in the
sidereal bodies of the element hydrogen. Not only are there vast
quantities of this element in the sun's atmosphere, but some
other suns appeared to show hydrogen lines almost exclusively in
their spectra.  Presently it appeared that the stars of which
this is true are those white stars, such as Sirius, which had
been conjectured to be the hottest; whereas stars that are only
red-hot, like our sun, show also the vapors of many other
elements, including iron and other metals.

In 1878 Professor J. Norman Lockyer, in a paper before the Royal
Society, called attention to the possible significance of this
series of observations. He urged that the fact of the sun showing
fewer elements than are observed here on the cool earth, while
stars much hotter than the sun show chiefly one element, and that
one hydrogen, the lightest of known elements, seemed to give
color to the possibility that our alleged elements are really
compounds, which at the temperature of the hottest stars may be
decomposed into hydrogen, the latter "element" itself being also
doubtless a compound, which might be resolved under yet more
trying conditions.

Here, then, was what might be termed direct experimental evidence
for the hypothesis of Prout.  Unfortunately, however, it is
evidence of a kind which only a few experts are competent to
discuss--so very delicate a matter is the spectral analysis of
the stars. What is still more unfortunate, the experts do not
agree among themselves as to the validity of Professor Lockyer's
conclusions. Some, like Professor Crookes, have accepted them
with acclaim, hailing Lockyer as "the Darwin of the inorganic
world," while others have sought a different explanation of the
facts he brings forward. As yet it cannot be said that the
controversy has been brought to final settlement.  Still, it is
hardly to be doubted that now, since the periodic law has seemed
to join hands with the spectroscope, a belief in the compound
nature of the so-called elements is rapidly gaining ground among
chemists.  More and more general becomes the belief that the
Daltonian atom is really a compound radical, and that back of the
seeming diversity of the alleged elements is a single form of
primordial matter.  Indeed, in very recent months, direct
experimental evidence for this view has at last come to hand,
through the study of radio-active substances.  In a later chapter
we shall have occasion to inquire how this came about.



IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY

ALBRECHT VON HALLER

An epoch in physiology was made in the eighteenth century by the
genius and efforts of Albrecht von Haller (1708-1777), of Berne,
who is perhaps as worthy of the title "The Great" as any
philosopher who has been so christened by his contemporaries
since the time of Hippocrates.  Celebrated as a physician, he was
proficient in various fields, being equally famed in his own time
as poet, botanist, and statesman, and dividing his attention
between art and science.

As a child Haller was so sickly that he was unable to amuse
himself with the sports and games common to boys of his age, and
so passed most of his time poring over books.  When ten years of
age he began writing poems in Latin and German, and at fifteen
entered the University of Tubingen.  At seventeen he wrote
learned articles in opposition to certain accepted doctrines, and
at nineteen he received his degree of doctor. Soon after this he
visited England, where his zeal in dissecting brought him under
suspicion of grave-robbery, which suspicion made it expedient for
him to return to the Continent.  After studying botany in Basel
for some time he made an extended botanical journey through
Switzerland, finally settling in his native city, Berne, as a
practising physician. During this time he did not neglect either
poetry or botany, publishing anonymously a collection of poems.

In 1736 he was called to Gottingen as professor of anatomy,
surgery, chemistry, and botany.  During his labors in the
university he never neglected his literary work, sometimes living
and sleeping for days and nights together in his library, eating
his meals while delving in his books, and sleeping only when
actually compelled to do so by fatigue. During all this time he
was in correspondence with savants from all over the world, and
it is said of him that he never left a letter of any kind
unanswered.

Haller's greatest contribution to medical science was his famous
doctrine of irritability, which has given him the name of "father
of modern nervous physiology," just as Harvey is called "the
father of the modern physiology of the blood." It has been said
of this famous doctrine of irritability that "it moved all the
minds of the century--and not in the departments of medicine
alone--in a way of which we of the present day have no
satisfactory conception, unless we compare it with our modern
Darwinism."[1]

The principle of general irritability had been laid down by
Francis Glisson (1597-1677) from deductive studies, but Haller
proved by experiments along the line of inductive methods that
this irritability was not common to all "fibre as well as to the
fluids of the body," but something entirely special, and peculiar
only to muscular substance. He distinguished between irritability
of muscles and sensibility of nerves. In 1747 he gave as the
three forces that produce muscular movements: elasticity, or
"dead nervous force"; irritability, or "innate nervous force";
and nervous force in itself.  And in 1752 he described one
hundred and ninety experiments for determining what parts of the
body possess "irritability"--that is, the property of contracting
when stimulated. His conclusion that this irritability exists in
muscular substance alone and is quite independent of the nerves
proceeding to it aroused a controversy that was never definitely
settled until late in the nineteenth century, when Haller's
theory was found to be entirely correct.

It was in pursuit of experiments to establish his theory of
irritability that Haller made his chief discoveries in embryology
and development. He proved that in the process of incubation of
the egg the first trace of the heart of the chick shows itself in
the thirty-eighth hour, and that the first trace of red blood
showed in the forty-first hour. By his investigations upon the
lower animals he attempted to confirm the theory that since the
creation of genus every individual is derived from a preceding
individual--the existing theory of preformation, in which he
believed, and which taught that "every individual is fully and
completely preformed in the germ, simply growing from microscopic
to visible proportions, without developing any new parts."

In physiology, besides his studies of the nervous system, Haller
studied the mechanism of respiration, refuting the teachings of
Hamberger (1697-1755), who maintained that the lungs contract
independently. Haller, however, in common with his
contemporaries, failed utterly to understand the true function of
the lungs.  The great physiologist's influence upon practical
medicine, while most profound, was largely indirect. He was a
theoretical rather than a practical physician, yet he is credited
with being the first physician to use the watch in counting the
pulse.


BATTISTA MORGAGNI AND MORBID ANATOMY

A great contemporary of Haller was Giovanni Battista Morgagni
(1682-1771), who pursued what Sydenham had neglected, the
investigation in anatomy, thus supplying a necessary counterpart
to the great Englishman's work.  Morgagni's investigations were
directed chiefly to the study of morbid anatomy--the study of the
structure of diseased tissue, both during life and post mortem,
in contrast to the normal anatomical structures. This work cannot
be said to have originated with him; for as early as 1679 Bonnet
had made similar, although less extensive, studies; and later
many investigators, such as Lancisi and Haller, had made
post-mortem studies.  But Morgagni's De sedibus et causis
morborum per anatomen indagatis was the largest, most accurate,
and best-illustrated collection of cases that had ever been
brought together, and marks an epoch in medical science. From the
time of the publication of Morgagni's researches, morbid anatomy
became a recognized branch of the medical science, and the effect
of the impetus thus given it has been steadily increasing since
that time.


WILLIAM HUNTER

William Hunter (1718-1783) must always be remembered as one of
the greatest physicians and anatomists of the eighteenth century,
and particularly as the first great teacher of anatomy in
England; but his fame has been somewhat overshadowed by that of
his younger brother John.

Hunter had been intended and educated for the Church, but on the
advice of the surgeon William Cullen he turned his attention to
the study of medicine. His first attempt at teaching was in 1746,
when he delivered a series of lectures on surgery for the Society
of Naval Practitioners.  These lectures proved so interesting and
instructive that he was at once invited to give others, and his
reputation as a lecturer was soon established. He was a natural
orator and story-teller, and he combined with these attractive
qualities that of thoroughness and clearness in demonstrations,
and although his lectures were two hours long he made them so
full of interest that his pupils seldom tired of listening.  He
believed that he could do greater good to the world by "publicly
teaching his art than by practising it," and even during the last
few days of his life, when he was so weak that his friends
remonstrated against it, he continued his teaching, fainting from
exhaustion at the end of his last lecture, which preceded his
death by only a few days.

For many years it was Hunter's ambition to establish a museum
where the study of anatomy, surgery, and medicine might be
advanced, and in 1765 he asked for a grant of a plot of ground
for this purpose, offering to spend seven thousand pounds on its,
erection besides endowing it with a professorship of anatomy. Not
being able to obtain this grant, however, he built a house, in
which were lecture and dissecting rooms, and his museum. In this
museum were anatomical preparations, coins, minerals, and
natural-history specimens.

Hunter's weakness was his love of controversy and his resentment
of contradiction.  This brought him into strained relations with
many of the leading physicians of his time, notably his own
brother John, who himself was probably not entirely free from
blame in the matter. Hunter is said to have excused his own
irritability on the grounds that being an anatomist, and
accustomed to "the passive submission of dead bodies,"
contradictions became the more unbearable. Many of the
physiological researches begun by him were carried on and
perfected by his more famous brother, particularly his
investigations of the capillaries, but he added much to the
anatomical knowledge of several structures of the body, notably
as to the structure of cartilages and joints.


JOHN HUNTER

In Abbot Islip's chapel in Westminster Abbey, close to the
resting-place of Ben Jonson, rest the remains of John Hunter
(1728-1793), famous in the annals of medicine as among the
greatest physiologists and surgeons that the world has ever
produced: a man whose discoveries and inventions are counted by
scores, and whose field of research was only limited by the
outermost boundaries of eighteenth-century science, although his
efforts were directed chiefly along the lines of his profession.

Until about twenty years of age young Hunter had shown little
aptitude for study, being unusually fond of out-door sports and
amusements; but about that time, realizing that some occupation
must be selected, he asked permission of his brother William to
attempt some dissections in his anatomical school in London.  To
the surprise of his brother he made this dissection unusually
well; and being given a second, he acquitted himself with such
skill that his brother at once predicted that he would become a
great anatomist.  Up to this time he had had no training of any
kind to prepare him for his professional career, and knew little
of Greek or Latin--languages entirely unnecessary for him, as he
proved in all of his life work.  Ottley tells the story that,
when twitted with this lack of knowledge of the "dead languages"
in after life, he said of his opponent, "I could teach him that
on the dead body which he never knew in any language, dead or
living."

By his second year in dissection he had become so skilful that he
was given charge of some of the classes in his brother's school;
in 1754 he became a surgeon's pupil in St. George's Hospital, and
two years later house-surgeon. Having by overwork brought on
symptoms that seemed to threaten consumption, he accepted the
position of staff-surgeon to an expedition to Belleisle in 1760,
and two years later was serving with the English army at
Portugal.  During all this time he was constantly engaged in
scientific researches, many of which, such as his observations of
gun-shot wounds, he put to excellent use in later life. On
returning to England much improved in health in 1763, he entered
at once upon his career as a London surgeon, and from that time
forward his progress was a practically uninterrupted series of
successes in his profession.

Hunter's work on the study of the lymphatics was of great service
to the medical profession.  This important net-work of minute
vessels distributed throughout the body had recently been made
the object of much study, and various students, including Haller,
had made extensive investigations since their discovery by
Asellius.  But Hunter, in 1758, was the first to discover the
lymphatics in the neck of birds, although it was his brother
William who advanced the theory that the function of these
vessels was that of absorbents. One of John Hunter's pupils,
William Hewson (1739-1774), first gave an account, in 1768, of
the lymphatics in reptiles and fishes, and added to his teacher's
investigations of the lymphatics in birds. These studies of the
lymphatics have been regarded, perhaps with justice, as Hunter's
most valuable contributions to practical medicine.

In 1767 he met with an accident by which he suffered a rupture of
the tendo Achillis--the large tendon that forms the attachment of
the muscles of the calf to the heel. From observations of this
accident, and subsequent experiments upon dogs, he laid the
foundation for the now simple and effective operation for the
cure of club feet and other deformities involving the tendons. 
In 1772 he moved into his residence at Earlscourt, Brompton,
where he gathered about him a great menagerie of animals, birds,
reptiles, insects, and fishes, which he used in his physiological
and surgical experiments. Here he performed a countless number of
experiments--more, probably, than "any man engaged in
professional practice has ever conducted." These experiments
varied in nature from observations of the habits of bees and
wasps to major surgical operations performed upon hedgehogs,
dogs, leopards, etc.  It is said that for fifteen years he kept a
flock of geese for the sole purpose of studying the process of
development in eggs.

Hunter began his first course of lectures in 1772, being forced
to do this because he had been so repeatedly misquoted, and
because he felt that he could better gauge his own knowledge in
this way. Lecturing was a sore trial to him, as he was extremely
diffident, and without writing out his lectures in advance he was
scarcely able to speak at all.  In this he presented a marked
contrast to his brother William, who was a fluent and brilliant
speaker. Hunter's lectures were at best simple readings of the
facts as he had written them, the diffident teacher seldom
raising his eyes from his manuscript and rarely stopping until
his complete lecture had been read through.  His lectures were,
therefore, instructive rather than interesting, as he used
infinite care in preparing them; but appearing before his classes
was so dreaded by him that he is said to have been in the habit
of taking a half-drachm of laudanum before each lecture to nerve
him for the ordeal. One is led to wonder by what name he shall
designate that quality of mind that renders a bold and fearless
surgeon like Hunter, who is undaunted in the face of hazardous
and dangerous operations, a stumbling, halting, and "frightened"
speaker before a little band of, at most, thirty young medical
students.  And yet this same thing is not unfrequently seen among
the boldest surgeons.


Hunter's Operation for the Cure of Aneurisms

It should be an object-lesson to those who, ignorantly or
otherwise, preach against the painless vivisection as practised
to-day, that by the sacrifice of a single deer in the cause of
science Hunter discovered a fact in physiology that has been the
means of saving thousands of human lives and thousands of human
bodies from needless mutilation. We refer to the discovery of the
"collateral circulation" of the blood, which led, among other
things, to Hunter's successful operation upon aneurisms.

Simply stated, every organ or muscle of the body is supplied by
one large artery, whose main trunk distributes the blood into its
lesser branches, and thence through the capillaries. Cutting off
this main artery, it would seem, should cut off entirely the
blood-supply to the particular organ which is supplied by this
vessel; and until the time of Hunter's demonstration this belief
was held by most physiologists. But nature has made a provision
for this possible stoppage of blood-supply from a single source,
and has so arranged that some of the small arterial branches
coming from the main supply-trunk are connected with other
arterial branches coming from some other supply-trunk. Under
normal conditions the main arterial trunks supply their
respective organs, the little connecting arterioles playing an
insignificant part. But let the main supply-trunk be cut off or
stopped for whatever reason, and a remarkable thing takes place.
The little connecting branches begin at once to enlarge and draw
blood from the neighboring uninjured supply-trunk, This
enlargement continues until at last a new route for the
circulation has been established, the organ no longer depending
on the now defunct original arterial trunk, but getting on as
well as before by this "collateral" circulation that has been
established.

The thorough understanding of this collateral circulation is one
of the most important steps in surgery, for until it was
discovered amputations were thought necessary in such cases as
those involving the artery supplying a leg or arm, since it was
supposed that, the artery being stopped, death of the limb and
the subsequent necessity for amputation were sure to follow.
Hunter solved this problem by a single operation upon a deer, and
his practicality as a surgeon led him soon after to apply this
knowledge to a certain class of surgical cases in a most
revolutionary and satisfactory manner.

What led to Hunter's far-reaching discovery was his investigation
as to the cause of the growth of the antlers of the deer. Wishing
to ascertain just what part the blood-supply on the opposite
sides of the neck played in the process of development, or,
perhaps more correctly, to see what effect cutting off the main
blood-supply would have, Hunter had one of the deer of Richmond
Park caught and tied, while he placed a ligature around one of
the carotid arteries--one of the two principal arteries that
supply the head with blood. He observed that shortly after this
the antler (which was only half grown and consequently very
vascular) on the side of the obliterated artery became cold to
the touch--from the lack of warmth-giving blood. There was
nothing unexpected in this, and Hunter thought nothing of it
until a few days later, when he found, to his surprise, that the
antler had become as warm as its fellow, and was apparently
increasing in size. Puzzled as to how this could be, and
suspecting that in some way his ligature around the artery had
not been effective, he ordered the deer killed, and on
examination was astonished to find that while his ligature had
completely shut off the blood-supply from the source of that
carotid artery, the smaller arteries had become enlarged so as to
supply the antler with blood as well as ever, only by a different
route.

Hunter soon had a chance to make a practical application of the
knowledge thus acquired.  This was a case of popliteal aneurism,
operations for which had heretofore proved pretty uniformly
fatal. An aneurism, as is generally understood, is an enlargement
of a certain part of an artery, this enlargement sometimes
becoming of enormous size, full of palpitating blood, and likely
to rupture with fatal results at any time.  If by any means the
blood can be allowed to remain quiet for even a few hours in this
aneurism it will form a clot, contract, and finally be absorbed
and disappear without any evil results. The problem of keeping
the blood quiet, with the heart continually driving it through
the vessel, is not a simple one, and in Hunter's time was
considered so insurmountable that some surgeons advocated
amputation of any member having an aneurism, while others cut
down upon the tumor itself and attempted to tie off the artery
above and below. The first of these operations maimed the patient
for life, while the second was likely to prove fatal.

In pondering over what he had learned about collateral
circulation and the time required for it to become fully
established, Hunter conceived the idea that if the blood-supply
was cut off from above the aneurism, thus temporarily preventing
the ceaseless pulsations from the heart, this blood would
coagulate and form a clot before the collateral circulation could
become established or could affect it.  The patient upon whom he
performed his now celebrated operation was afflicted with a
popliteal aneurism--that is, the aneurism was located on the
large popliteal artery just behind the knee-joint. Hunter,
therefore, tied off the femoral, or main supplying artery in the
thigh, a little distance above the aneurism. The operation was
entirely successful, and in six weeks' time the patient was able
to leave the hospital, and with two sound limbs. Naturally the
simplicity and success of this operation aroused the attention of
Europe, and, alone, would have made the name of Hunter immortal
in the annals of surgery.  The operation has ever since been
called the "Hunterian" operation for aneurism, but there is
reason to believe that Dominique Anel (born about 1679) performed
a somewhat similar operation several years earlier. It is
probable, however, that Hunter had never heard of this work of
Anel, and that his operation was the outcome of his own
independent reasoning from the facts he had learned about
collateral circulation. Furthermore, Hunter's mode of operation
was a much better one than Anel's, and, while Anel's must claim
priority, the credit of making it widely known will always be
Hunter's.

The great services of Hunter were recognized both at home and
abroad, and honors and positions of honor and responsibility were
given him. In 1776 he was appointed surgeon-extraordinary to the
king; in 1783 he was elected a member of the Royal Society of
Medicine and of the Royal Academy of Surgery at Paris; in 1786 he
became deputy surgeon-general of the army; and in 1790 he was
appointed surgeon-general and inspector-general of hospitals. All
these positions he filled with credit, and he was actively
engaged in his tireless pursuit of knowledge and in discharging
his many duties when in October, 1793, he was stricken while
addressing some colleagues, and fell dead in the arms of a
fellow-physician.


LAZZARO SPALLANZANI

Hunter's great rival among contemporary physiologists was the
Italian Lazzaro Spallanzani (1729-1799), one of the most
picturesque figures in the history of science. He was not
educated either as a scientist or physician, devoting, himself at
first to philosophy and the languages, afterwards studying law,
and later taking orders. But he was a keen observer of nature and
of a questioning and investigating mind, so that he is remembered
now chiefly for his discoveries and investigations in the
biological sciences. One important demonstration was his
controversion of the theory of abiogenesis, or "spontaneous
generation," as propounded by Needham and Buffon.  At the time of
Needham's experiments it had long been observed that when animal
or vegetable matter had lain in water for a little time--long
enough for it to begin to undergo decomposition--the water became
filled with microscopic creatures, the "infusoria animalculis."
This would tend to show, either that the water or the animal or
vegetable substance contained the "germs" of these minute
organisms, or else that they were generated spontaneously. It was
known that boiling killed these animalcules, and Needham agreed,
therefore, that if he first heated the meat or vegetables, and
also the water containing them, and then placed them in
hermetically scaled jars--if he did this, and still the
animalcules made their appearance, it would be proof-positive
that they had been generated spontaneously.  Accordingly be made
numerous experiments, always with the same results--that after a
few days the water was found to swarm with the microscopic
creatures. The thing seemed proven beyond question--providing, of
course, that there had been no slips in the experiments.

But Abbe Spallanzani thought that he detected such slips in
Needham's experiment.  The possibility of such slips might come
in several ways:  the contents of the jar might not have been
boiled for a sufficient length of time to kill all the germs, or
the air might not have been excluded completely by the sealing
process. To cover both these contingencies, Spallanzani first
hermetically sealed the glass vessels and then boiled them for
three-quarters of an hour. Under these circumstances no
animalcules ever made their appearance--a conclusive
demonstration that rendered Needham's grounds for his theory at
once untenable.[2]

Allied to these studies of spontaneous generation were
Spallanzani's experiments and observations on the physiological
processes of generation among higher animals.  He experimented
with frogs, tortoises, and dogs; and settled beyond question the
function of the ovum and spermatozoon. Unfortunately he
misinterpreted the part played by the spermatozoa in believing
that their surrounding fluid was equally active in the
fertilizing process, and it was not until some forty years later
(1824) that Dumas corrected this error.


THE CHEMICAL THEORY OF DIGESTION

Among the most interesting researches of Spallanzani were his
experiments to prove that digestion, as carried on in the
stomach, is a chemical process.  In this he demonstrated, as Rene
Reaumur had attempted to demonstrate, that digestion could be
carried on outside the walls of the stomach as an ordinary
chemical reaction, using the gastric juice as the reagent for
performing the experiment. The question as to whether the stomach
acted as a grinding or triturating organ, rather than as a
receptacle for chemical action, had been settled by Reaumur and
was no longer a question of general dispute. Reaumur had
demonstrated conclusively that digestion would take place in the
stomach in the same manner and the same time if the substance to
be digested was protected from the peristalic movements of the
stomach and subjected to the action of the gastric juice only. He
did this by introducing the substances to be digested into the
stomach in tubes, and thus protected so that while the juices of
the stomach could act upon them freely they would not be affected
by any movements of the organ.

Following up these experiments, he attempted to show that
digestion could take place outside the body as well as in it, as
it certainly should if it were a purely chemical process. He
collected quantities of gastric juice, and placing it in suitable
vessels containing crushed grain or flesh, kept the mixture at
about the temperature of the body for several hours. After
repeated experiments of this kind, apparently conducted with
great care, Reaumur reached the conclusion that "the gastric
juice has no more effect out of the living body in dissolving or
digesting the food than water, mucilage, milk, or any other bland
fluid."[3] Just why all of these experiments failed to
demonstrate a fact so simple does not appear; but to Spallanzani,
at least, they were by no means conclusive, and he proceeded to
elaborate upon the experiments of Reaumur.  He made his
experiments in scaled tubes exposed to a certain degree of heat,
and showed conclusively that the chemical process does go on,
even when the food and gastric juice are removed from their
natural environment in the stomach. In this he was opposed by
many physiologists, among them John Hunter, but the truth of his
demonstrations could not be shaken, and in later years we find
Hunter himself completing Spallanzani's experiments by his
studies of the post-mortem action of the gastric juice upon the
stomach walls.

That Spallanzani's and Hunter's theories of the action of the
gastric juice were not at once universally accepted is shown by
an essay written by a learned physician in 1834. In speaking of
some of Spallanzani's demonstrations, he writes: "In some of the
experiments, in order to give the flesh or grains steeped in the
gastric juice the same temperature with the body, the phials were
introduced under the armpits. But this is not a fair mode of
ascertaining the effects of the gastric juice out of the body;
for the influence which life may be supposed to have on the
solution of the food would be secured in this case.  The
affinities connected with life would extend to substances in
contact with any part of the system: substances placed under the
armpits are not placed at least in the same circumstances with
those unconnected with a living animal." But just how this writer
reaches the conclusion that "the experiments of Reaumur and
Spallanzani give no evidence that the gastric juice has any
peculiar influence more than water or any other bland fluid in
digesting the food"[4] is difficult to understand.

The concluding touches were given to the new theory of digestion
by John Hunter, who, as we have seen, at first opposed
Spallanzani, but who finally became an ardent champion of the
chemical theory. Hunter now carried Spallanzani's experiments
further and proved the action of the digestive fluids after
death. For many years anatomists had been puzzled by pathological
lesion of the stomach, found post mortem, when no symptoms of any
disorder of the stomach had been evinced during life. Hunter
rightly conceived that these lesions were caused by the action of
the gastric juice, which, while unable to act upon the living
tissue, continued its action chemically after death, thus
digesting the walls of the stomach in which it had been formed. 
And, as usual with his observations, be turned this discovery to
practical use in accounting for certain phenomena of digestion. 
The following account of the stomach being digested after death
was written by Hunter at the desire of Sir John Pringle, when he
was president of the Royal Society, and the circumstance which
led to this is as follows: "I was opening, in his presence, the
body of a patient of his own, where the stomach was in part
dissolved, which appeared to him very unaccountable, as there had
been no previous symptom that could have led him to suspect any
disease in the stomach. I took that opportunity of giving him my
ideas respecting it, and told him that I had long been making
experiments on digestion, and considered this as one of the facts
which proved a converting power in the gastric juice. . . . There
are a great many powers in nature which the living principle does
not enable the animal matter, with which it is combined, to
resist--viz., the mechanical and most of the strongest chemical
solvents. It renders it, however, capable of resisting the powers
of fermentation, digestion, and perhaps several others, which are
well known to act on the same matter when deprived of the living
principle and entirely to decompose it.  "

Hunter concludes his paper with the following paragraph: "These
appearances throw considerable light on the principle of
digestion, and show that it is neither a mechanical power, nor
contractions of the stomach, nor heat, but something secreted in
the coats of the stomach, and thrown into its cavity, which there
animalizes the food or assimilates it to the nature of the blood.
The power of this juice is confined or limited to certain
substances, especially of the vegetable and animal kingdoms; and
although this menstruum is capable of acting independently of the
stomach, yet it is indebted to that viscus for its
continuance.[5]


THE FUNCTION OF RESPIRATION

It is a curious commentary on the crude notions of mechanics of
previous generations that it should have been necessary to prove
by experiment that the thin, almost membranous stomach of a
mammal has not the power to pulverize, by mere attrition, the
foods that are taken into it.  However, the proof was now for the
first time forthcoming, and the question of the general character
of the function of digestion was forever set at rest. Almost
simultaneously with this great advance, corresponding progress
was made in an allied field:  the mysteries of respiration were
at last cleared up, thanks to the new knowledge of chemistry. The
solution of the problem followed almost as a matter of course
upon the advances of that science in the latter part of the
century. Hitherto no one since Mayow, of the previous century,
whose flash of insight had been strangely overlooked and
forgotten, had even vaguely surmised the true function of the
lungs. The great Boerhaave had supposed that respiration is
chiefly important as an aid to the circulation of the blood; his
great pupil, Haller, had believed to the day of his death in 1777
that the main purpose of the function is to form the voice. No
genius could hope to fathom the mystery of the lungs so long as
air was supposed to be a simple element, serving a mere
mechanical purpose in the economy of the earth.

But the discovery of oxygen gave the clew, and very soon all the
chemists were testing the air that came from the lungs--Dr.
Priestley, as usual, being in the van.  His initial experiments
were made in 1777, and from the outset the problem was as good as
solved. Other experimenters confirmed his results in all their
essentials--notably Scheele and Lavoisier and Spallanzani and
Davy.  It was clearly established that there is chemical action
in the contact of the air with the tissue of the lungs; that some
of the oxygen of the air disappears, and that carbonic-acid gas
is added to the inspired air.  It was shown, too, that the blood,
having come in contact with the air, is changed from black to red
in color. These essentials were not in dispute from the first. 
But as to just what chemical changes caused these results was the
subject of controversy. Whether, for example, oxygen is actually
absorbed into the blood, or whether it merely unites with carbon
given off from the blood, was long in dispute.

Each of the main disputants was biased by his own particular
views as to the moot points of chemistry.  Lavoisier, for
example, believed oxygen gas to be composed of a metal oxygen
combined with the alleged element heat; Dr. Priestley thought it
a compound of positive electricity and phlogiston; and Humphry
Davy, when he entered the lists a little later, supposed it to be
a compound of oxygen and light. Such mistaken notions naturally
complicated matters and delayed a complete understanding of the
chemical processes of respiration. It was some time, too, before
the idea gained acceptance that the most important chemical
changes do not occur in the lungs themselves, but in the ultimate
tissues.  Indeed, the matter was not clearly settled at the close
of the century.  Nevertheless, the problem of respiration had
been solved in its essentials.  Moreover, the vastly important
fact had been established that a process essentially identical
with respiration is necessary to the existence not only of all
creatures supplied with lungs, but to fishes, insects, and even
vegetables--in short, to every kind of living organism.


ERASMUS DARWIN AND VEGETABLE PHYSIOLOGY

Some interesting experiments regarding vegetable respiration were
made just at the close of the century by Erasmus Darwin, and
recorded in his Botanic Garden as a foot-note to the verse:

"While spread in air the leaves respiring play."


These notes are worth quoting at some length, as they give a
clear idea of the physiological doctrines of the time (1799),
while taking advance ground as to the specific matter in
question:


"There have been various opinions," Darwin says, "concerning the
use of the leaves of plants in the vegetable economy.  Some have
contended that they are perspiratory organs.  This does not seem
probable from an experiment of Dr. Hales, Vegetable Statics, p. 
30.  He, found, by cutting off branches of trees with apples on
them and taking off the leaves, that an apple exhaled about as
much as two leaves the surfaces of which were nearly equal to the
apple; whence it would appear that apples have as good a claim to
be termed perspiratory organs as leaves. Others have believed
them excretory organs of excrementitious juices, but as the vapor
exhaled from vegetables has no taste, this idea is no more
probable than the other; add to this that in most weathers they
do not appear to perspire or exhale at all.

"The internal surface of the lungs or air-vessels in men is said
to be equal to the external surface of the whole body, or almost
fifteen square feet; on this surface the blood is exposed to the
influence of the respired air through the medium, however, of a
thin pellicle; by this exposure to the air it has its color
changed from deep red to bright scarlet, and acquires something
so necessary to the existence of life that we can live scarcely a
minute without this wonderful process.

"The analogy between the leaves of plants and the lungs or gills
of animals seems to embrace so many circumstances that we can
scarcely withhold our consent to their performing similar
offices.

"1.  The great surface of leaves compared to that of the trunk
and branches of trees is such that it would seem to be an organ
well adapted for the purpose of exposing the vegetable juices to
the influence of the air; this, however, we shall see afterwards
is probably performed only by their upper surfaces, yet even in
this case the surface of the leaves in general bear a greater
proportion to the surface of the tree than the lungs of animals
to their external surfaces.

"2.  In the lung of animals the blood, after having been exposed
to the air in the extremities of the pulmonary artery, is changed
in color from deep red to bright scarlet, and certainly in some
of its essential properties it is then collected by the pulmonary
vein and returned to the heart. To show a similarity of
circumstances in the leaves of plants, the following experiment
was made, June 24, 1781.  A stalk with leaves and seed-vessels of
large spurge (Euphorbia helioscopia) had been several days placed
in a decoction of madder (Rubia tinctorum) so that the lower part
of the stem and two of the undermost leaves were immersed in it.
After having washed the immersed leaves in clear water I could
readily discover the color of the madder passing along the middle
rib of each leaf.  The red artery was beautifully visible on the
under and on the upper surface of the leaf; but on the upper side
many red branches were seen going from it to the extremities of
the leaf, which on the other side were not visible except by
looking through it against the light. On this under side a system
of branching vessels carrying a pale milky fluid were seen coming
from the extremities of the leaf, and covering the whole under
side of it, and joining two large veins, one on each side of the
red artery in the middle rib of the leaf, and along with it
descending to the foot-stalk or petiole. On slitting one of these
leaves with scissors, and having a magnifying-glass ready, the
milky blood was seen oozing out of the returning veins on each
side of the red artery in the middle rib, but none of the red
fluid from the artery.

"All these appearances were more easily seen in a leaf of Picris
treated in the same manner; for in this milky plant the stems and
middle rib of the leaves are sometimes naturally colored reddish,
and hence the color of the madder seemed to pass farther into the
ramifications of their leaf-arteries, and was there beautifully
visible with the returning branches of milky veins on each side."


Darwin now goes on to draw an incorrect inference from his
observations:


"3.  From these experiments," he says, "the upper surface of the
leaf appeared to be the immediate organ of respiration, because
the colored fluid was carried to the extremities of the leaf by
vessels most conspicuous on the upper surface, and there changed
into a milky fluid, which is the blood of the plant, and then
returned by concomitant veins on the under surface, which were
seen to ooze when divided with scissors, and which, in Picris,
particularly, render the under surface of the leaves greatly
whiter than the upper one."


But in point of fact, as studies of a later generation were to
show, it is the under surface of the leaf that is most abundantly
provided with stomata, or "breathing-pores." From the stand-point
of this later knowledge, it is of interest to follow our author a
little farther, to illustrate yet more fully the possibility of
combining correct observations with a faulty inference.


"4.  As the upper surface of leaves constitutes the organ of
respiration, on which the sap is exposed in the termination of
arteries beneath a thin pellicle to the action of the atmosphere,
these surfaces in many plants strongly repel moisture, as cabbage
leaves, whence the particles of rain lying over their surfaces
without touching them, as observed by Mr. Melville (Essays
Literary and Philosophical:  Edinburgh), have the appearance of
globules of quicksilver.  And hence leaves with the upper
surfaces on water wither as soon as in the dry air, but continue
green for many days if placed with the under surface on water, as
appears in the experiments of Monsieur Bonnet (Usage des
Feuilles). Hence some aquatic plants, as the water-lily
(Nymphoea), have the lower sides floating on the water, while the
upper surfaces remain dry in the air.

"5.  As those insects which have many spiracula, or breathing
apertures, as wasps and flies, are immediately suffocated by
pouring oil upon them, I carefully covered with oil the surfaces
of several leaves of phlomis, of Portugal laurel, and balsams,
and though it would not regularly adhere, I found them all die in
a day or two.

"It must be added that many leaves are furnished with muscles
about their foot-stalks, to turn their surfaces to the air or
light, as mimosa or Hedysarum gyrans.  From all these analogies I
think there can be no doubt but that leaves of trees are their
lungs, giving out a phlogistic material to the atmosphere, and
absorbing oxygen, or vital air.

"6.  The great use of light to vegetation would appear from this
theory to be by disengaging vital air from the water which they
perspire, and thence to facilitate its union with their blood
exposed beneath the thin surface of their leaves; since when pure
air is thus applied it is probable that it can be more readily
absorbed.  Hence, in the curious experiments of Dr. Priestley and
Mr. Ingenhouz, some plants purified less air than others--that
is, they perspired less in the sunshine; and Mr. Scheele found
that by putting peas into water which about half covered them
they converted the vital air into fixed air, or carbonic-acid
gas, in the same manner as in animal respiration.

"7.  The circulation in the lungs or leaves of plants is very
similar to that of fish.  In fish the blood, after having passed
through their gills, does not return to the heart as from the
lungs of air-breathing animals, but the pulmonary vein taking the
structure of an artery after having received the blood from the
gills, which there gains a more florid color, distributes it to
the other parts of their bodies. The same structure occurs in the
livers of fish, whence we see in those animals two circulations
independent of the power of the heart--viz., that beginning at
the termination of the veins of the gills and branching through
the muscles, and that which passes through the liver; both which
are carried on by the action of those respective arteries and
veins."[6]

Darwin is here a trifle fanciful in forcing the analogy between
plants and animals.  The circulatory system of plants is really
not quite so elaborately comparable to that of fishes as he
supposed. But the all-important idea of the uniformity underlying
the seeming diversity of Nature is here exemplified, as elsewhere
in the writings of Erasmus Darwin; and, more specifically, a
clear grasp of the essentials of the function of respiration is
fully demonstrated.


ZOOLOGY AT THE CLOSE OF THE EIGHTEENTH CENTURY


Several causes conspired to make exploration all the fashion
during the closing epoch of the eighteenth century. New aid to
the navigator had been furnished by the perfected compass and
quadrant, and by the invention of the chronometer; medical
science had banished scurvy, which hitherto had been a perpetual
menace to the voyager; and, above all, the restless spirit of the
age impelled the venturesome to seek novelty in fields altogether
new.  Some started for the pole, others tried for a northeast or
northwest passage to India, yet others sought the great
fictitious antarctic continent told of by tradition. All these of
course failed of their immediate purpose, but they added much to
the world's store of knowledge and its fund of travellers' tales.

Among all these tales none was more remarkable than those which
told of strange living creatures found in antipodal lands. And
here, as did not happen in every field, the narratives were often
substantiated by the exhibition of specimens that admitted no
question. Many a company of explorers returned more or less laden
with such trophies from the animal and vegetable kingdoms, to the
mingled astonishment, delight, and bewilderment of the closet
naturalists. The followers of Linnaeus in the "golden age of
natural history," a few decades before, had increased the number
of known species of fishes to about four hundred, of birds to one
thousand, of insects to three thousand, and of plants to ten
thousand. But now these sudden accessions from new territories
doubled the figure for plants, tripled it for fish and birds, and
brought the number of described insects above twenty thousand. 
Naturally enough, this wealth of new material was sorely puzzling
to the classifiers. The more discerning began to see that the
artificial system of Linnaeus, wonderful and useful as it had
been, must be advanced upon before the new material could be
satisfactorily disposed of. The way to a more natural system,
based on less arbitrary signs, had been pointed out by Jussieu in
botany, but the zoologists were not prepared to make headway
towards such a system until they should gain a wider
understanding of the organisms with which they had to deal
through comprehensive studies of anatomy. Such studies of
individual forms in their relations to the entire scale of
organic beings were pursued in these last decades of the century,
but though two or three most important generalizations were
achieved (notably Kaspar Wolff's conception of the cell as the
basis of organic life, and Goethe's all-important doctrine of
metamorphosis of parts), yet, as a whole, the work of the
anatomists of the period was germinative rather than
fruit-bearing. Bichat's volumes, telling of the recognition of
the fundamental tissues of the body, did not begin to appear till
the last year of the century. The announcement by Cuvier of the
doctrine of correlation of parts bears the same date, but in
general the studies of this great naturalist, which in due time
were to stamp him as the successor of Linnaeus, were as yet only
fairly begun.



 V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY

CUVIER AND THE CORRELATION OF PARTS

We have seen that the focal points of the physiological world
towards the close of the eighteenth century were Italy and
England, but when Spallanzani and Hunter passed away the scene
shifted to France.  The time was peculiarly propitious, as the
recent advances in many lines of science had brought fresh data
for the student of animal life which were in need of
classification, and, as several minds capable of such a task were
in the field, it was natural that great generalizations should
have come to be quite the fashion. Thus it was that Cuvier came
forward with a brand-new classification of the animal kingdom,
establishing four great types of being, which he called
vertebrates, mollusks, articulates, and radiates. Lamarck had
shortly before established the broad distinction between animals
with and those without a backbone; Cuvier's Classification
divided the latter--the invertebrates--into three minor groups.
And this division, familiar ever since to all students of
zoology, has only in very recent years been supplanted, and then
not by revolution, but by a further division, which the elaborate
recent studies of lower forms of life seemed to make desirable.

In the course of those studies of comparative anatomy which led
to his new classification, Cuvier's attention was called
constantly to the peculiar co-ordination of parts in each
individual organism. Thus an animal with sharp talons for
catching living prey--as a member of the cat tribe--has also
sharp teeth, adapted for tearing up the flesh of its victim, and
a particular type of stomach, quite different from that of
herbivorous creatures. This adaptation of all the parts of the
animal to one another extends to the most diverse parts of the
organism, and enables the skilled anatomist, from the observation
of a single typical part, to draw inferences as to the structure
of the entire animal--a fact which was of vast aid to Cuvier in
his studies of paleontology. It did not enable Cuvier, nor does
it enable any one else, to reconstruct fully the extinct animal
from observation of a single bone, as has sometimes been
asserted, but what it really does establish, in the hands of an
expert, is sufficiently astonishing.

"While the study of the fossil remains of the greater quadrupeds
is more satisfactory," he writes, "by the clear results which it
affords, than that of the remains of other animals found in a
fossil state, it is also complicated with greater and more
numerous difficulties. Fossil shells are usually found quite
entire, and retaining all the characters requisite for comparing
them with the specimens contained in collections of natural
history, or represented in the works of naturalists. Even the
skeletons of fishes are found more or less entire, so that the
general forms of their bodies can, for the most part, be
ascertained, and usually, at least, their generic and specific
characters are determinable, as these are mostly drawn from their
solid parts. In quadrupeds, on the contrary, even when their
entire skeletons are found, there is great difficulty in
discovering their distinguishing characters, as these are chiefly
founded upon their hairs and colors and other marks which have
disappeared previous to their incrustation. It is also very rare
to find any fossil skeletons of quadrupeds in any degree
approaching to a complete state, as the strata for the most part
only contain separate bones, scattered confusedly and almost
always broken and reduced to fragments, which are the only means
left to naturalists for ascertaining the species or genera to
which they have belonged.

"Fortunately comparative anatomy, when thoroughly understood,
enables us to surmount all these difficulties, as a careful
application of its principles instructs us in the correspondences
and dissimilarities of the forms of organized bodies of different
kinds, by which each may be rigorously ascertained from almost
every fragment of its various parts and organs.

"Every organized individual forms an entire system of its own,
all the parts of which naturally correspond, and concur to
produce a certain definite purpose, by reciprocal reaction, or by
combining towards the same end.  Hence none of these separate
parts can change their forms without a corresponding change in
the other parts of the same animal, and consequently each of
these parts, taken separately, indicates all the other parts to
which it has belonged.  Thus, as I have elsewhere shown, if the
viscera of an animal are so organized as only to be fitted for
the digestion of recent flesh, it is also requisite that the jaws
should be so constructed as to fit them for devouring prey; the
claws must be constructed for seizing and tearing it to pieces;
the teeth for cutting and dividing its flesh; the entire system
of the limbs, or organs of motion, for pursuing and overtaking
it; and the organs of sense for discovering it at a distance.
Nature must also have endowed the brain of the animal with
instincts sufficient for concealing itself and for laying plans
to catch its necessary victims.  . . . . . . . . .

"To enable the animal to carry off its prey when seized, a
corresponding force is requisite in the muscles which elevate the
head, and this necessarily gives rise to a determinate form of
the vertebrae to which these muscles are attached and of the
occiput into which they are inserted. In order that the teeth of
a carnivorous animal may be able to cut the flesh, they require
to be sharp, more or less so in proportion to the greater or less
quantity of flesh that they have to cut. It is requisite that
their roots should be solid and strong, in proportion to the
quantity and size of the bones which they have to break to
pieces. The whole of these circumstances must necessarily
influence the development and form of all the parts which
contribute to move the jaws. . . . . . . . . .

After these observations, it will be easily seen that similar
conclusions may be drawn with respect to the limbs of carnivorous
animals, which require particular conformations to fit them for
rapidity of motion in general; and that similar considerations
must influence the forms and connections of the vertebrae and
other bones constituting the trunk of the body, to fit them for
flexibility and readiness of motion in all directions. The bones
also of the nose, of the orbit, and of the ears require certain
forms and structures to fit them for giving perfection to the
senses of smell, sight, and hearing, so necessary to animals of
prey. In short, the shape and structure of the teeth regulate the
forms of the condyle, of the shoulder-blade, and of the claws, in
the same manner as the equation of a curve regulates all its
other properties; and as in regard to any particular curve all
its properties may be ascertained by assuming each separate
property as the foundation of a particular equation, in the same
manner a claw, a shoulder-blade, a condyle, a leg or arm bone, or
any other bone separately considered, enables us to discover the
description of teeth to which they have belonged; and so also
reciprocally we may determine the forms of the other bones from
the teeth.  Thus commencing our investigations by a careful
survey of any one bone by itself, a person who is sufficiently
master of the laws of organic structure may, as it were,
reconstruct the whole animal to which that bone belonged."[1]

We have already pointed out that no one is quite able to perform
the necromantic feat suggested in the last sentence; but the
exaggeration is pardonable in the enthusiast to whom the
principle meant so much and in whose hands it extended so far.

Of course this entire principle, in its broad outlines, is
something with which every student of anatomy had been familiar
from the time when anatomy was first studied, but the full
expression of the "law of co-ordination," as Cuvier called it,
had never been explicitly made before; and, notwithstanding its
seeming obviousness, the exposition which Cuvier made of it in
the introduction to his classical work on comparative anatomy,
which was published during the first decade of the nineteenth
century, ranks as a great discovery. It is one of those
generalizations which serve as guideposts to other discoveries.


BICHAT AND THE BODILY TISSUES

Much the same thing may be said of another generalization
regarding the animal body, which the brilliant young French
physician Marie Francois Bichat made in calling attention to the
fact that each vertebrate organism, including man, has really two
quite different sets of organs--one set under volitional control,
and serving the end of locomotion, the other removed from
volitional control, and serving the ends of the "vital processes"
of digestion, assimilation, and the like. He called these sets of
organs the animal system and the organic system, respectively. 
The division thus pointed out was not quite new, for Grimaud,
professor of physiology in the University of Montpellier, had
earlier made what was substantially the same classification of
the functions into "internal or digestive and external or
locomotive"; but it was Bichat's exposition that gave currency to
the idea.

Far more important, however, was another classification which
Bichat put forward in his work on anatomy, published just at the
beginning of the last century.  This was the division of all
animal structures into what Bichat called tissues, and the
pointing out that there are really only a few kinds of these in
the body, making up all the diverse organs. Thus muscular organs
form one system; membranous organs another; glandular organs a
third; the vascular mechanism a fourth, and so on.  The
distinction is so obvious that it seems rather difficult to
conceive that it could have been overlooked by the earliest
anatomists; but, in point of fact, it is only obvious because now
it has been familiarly taught for almost a century. It had never
been given explicit expression before the time of Bichat, though
it is said that Bichat himself was somewhat indebted for it to
his master, Desault, and to the famous alienist Pinel.

However that may be, it is certain that all subsequent anatomists
have found Bichat's classification of the tissues of the utmost
value in their studies of the animal functions. Subsequent
advances were to show that the distinction between the various
tissues is not really so fundamental as Bichat supposed, but that
takes nothing from the practical value of the famous
classification.

It was but a step from this scientific classification of tissues
to a similar classification of the diseases affecting them, and
this was one of the greatest steps towards placing medicine on
the plane of an exact science. This subject of these branches
completely fascinated Bichat, and he exclaimed, enthusiastically: 
"Take away some fevers and nervous trouble, and all else belongs
to the kingdom of pathological anatomy." But out of this
enthusiasm came great results.  Bichat practised as he preached,
and, believing that it was only possible to understand disease by
observing the symptoms carefully at the bedside, and, if the
disease terminated fatally, by post-mortem examination, he was so
arduous in his pursuit of knowledge that within a period of less
than six months he had made over six hundred autopsies--a record
that has seldom, if ever, been equalled. Nor were his efforts
fruitless, as a single example will suffice to show. By his
examinations he was able to prove that diseases of the chest,
which had formerly been classed under the indefinite name
"peripneumonia," might involve three different structures, the
pleural sac covering the lungs, the lung itself, and the
bronchial tubes, the diseases affecting these organs being known
respectively as pleuritis, pneumonia, and bronchitis, each one
differing from the others as to prognosis and treatment. The
advantage of such an exact classification needs no demonstration.


LISTER AND THE PERFECTED MICROSCOPE

At the same time when these broad macroscopical distinctions were
being drawn there were other workers who were striving to go even
deeper into the intricacies of the animal mechanism with the aid
of the microscope.  This undertaking, however, was beset with
very great optical difficulties, and for a long time little
advance was made upon the work of preceding generations. Two
great optical barriers, known technically as spherical and
chromatic aberration--the one due to a failure of the rays of
light to fall all in one plane when focalized through a lens, the
other due to the dispersive action of the lens in breaking the
white light into prismatic colors--confronted the makers of
microscopic lenses, and seemed all but insuperable. The making of
achromatic lenses for telescopes had been accomplished, it is
true, by Dolland in the previous century, by the union of lenses
of crown glass with those of flint glass, these two materials
having different indices of refraction and dispersion. But, aside
from the mechanical difficulties which arise when the lens is of
the minute dimensions required for use with the microscope, other
perplexities are introduced by the fact that the use of a wide
pencil of light is a desideratum, in order to gain sufficient
illumination when large magnification is to be secured.

In the attempt to overcome those difficulties, the foremost
physical philosophers of the time came to the aid of the best
opticians. Very early in the century, Dr. (afterwards Sir David)
Brewster, the renowned Scotch physicist, suggested that certain
advantages might accrue from the use of such gems as have high
refractive and low dispersive indices, in place of lenses made of
glass. Accordingly lenses were made of diamond, of sapphire, and
so on, and with some measure of success.  But in 1812 a much more
important innovation was introduced by Dr. William Hyde
Wollaston, one of the greatest and most versatile, and, since the
death of Cavendish, by far the most eccentric of English natural
philosophers. This was the suggestion to use two plano-convex
lenses, placed at a prescribed distance apart, in lieu of the
single double-convex lens generally used.  This combination
largely overcame the spherical aberration, and it gained
immediate fame as the "Wollaston doublet."

To obviate loss of light in such a doublet from increase of
reflecting surfaces, Dr. Brewster suggested filling the
interspace between the two lenses with a cement having the same
index of refraction as the lenses themselves--an improvement of
manifest advantage. An improvement yet more important was made by
Dr. Wollaston himself in the introduction of the diaphragm to
limit the field of vision between the lenses, instead of in front
of the anterior lens.  A pair of lenses thus equipped Dr.
Wollaston called the periscopic microscope. Dr. Brewster
suggested that in such a lens the same object might be attained
with greater ease by grinding an equatorial groove about a thick
or globular lens and filling the groove with an opaque cement.
This arrangement found much favor, and came subsequently to be
known as a Coddington lens, though Mr. Coddington laid no claim
to being its inventor.

Sir John Herschel, another of the very great physicists of the
time, also gave attention to the problem of improving the
microscope, and in 1821 he introduced what was called an
aplanatic combination of lenses, in which, as the name implies,
the spherical aberration was largely done away with. It was
thought that the use of this Herschel aplanatic combination as an
eyepiece, combined with the Wollaston doublet for the objective,
came as near perfection as the compound microscope was likely
soon to come. But in reality the instrument thus constructed,
though doubtless superior to any predecessor, was so defective
that for practical purposes the simple microscope, such as the
doublet or the Coddington, was preferable to the more complicated
one.

Many opticians, indeed, quite despaired of ever being able to
make a satisfactory refracting compound microscope, and some of
them had taken up anew Sir Isaac Newton's suggestion in reference
to a reflecting microscope.  In particular, Professor Giovanni
Battista Amici, a very famous mathematician and practical
optician of Modena, succeeded in constructing a reflecting
microscope which was said to be superior to any compound
microscope of the time, though the events of the ensuing years
were destined to rob it of all but historical value. For there
were others, fortunately, who did not despair of the
possibilities of the refracting microscope, and their efforts
were destined before long to be crowned with a degree of success
not even dreamed of by any preceding generation.

The man to whom chief credit is due for directing those final
steps that made the compound microscope a practical implement
instead of a scientific toy was the English amateur optician
Joseph Jackson Lister.  Combining mathematical knowledge with
mechanical ingenuity, and having the practical aid of the
celebrated optician Tulley, he devised formulae for the
combination of lenses of crown glass with others of flint glass,
so adjusted that the refractive errors of one were corrected or
compensated by the other, with the result of producing lenses of
hitherto unequalled powers of definition; lenses capable of
showing an image highly magnified, yet relatively free from those
distortions and fringes of color that had heretofore been so
disastrous to true interpretation of magnified structures.

Lister had begun his studies of the lens in 1824, but it was not
until 1830 that he contributed to the Royal Society the famous
paper detailing his theories and experiments. Soon after this
various continental opticians who had long been working along
similar lines took the matter up, and their expositions, in
particular that of Amici, introduced the improved compound
microscope to the attention of microscopists everywhere. And it
required but the most casual trial to convince the experienced
observers that a new implement of scientific research had been
placed in their hands which carried them a long step nearer the
observation of the intimate physical processes which lie at the
foundation of vital phenomena.  For the physiologist this
perfection of the compound microscope had the same significance
that the, discovery of America had for the fifteenth-century
geographers--it promised a veritable world of utterly novel
revelations. Nor was the fulfilment of that promise long delayed.

Indeed, so numerous and so important were the discoveries now
made in the realm of minute anatomy that the rise of histology to
the rank of an independent science may be said to date from this
period. Hitherto, ever since the discovery of magnifying-glasses,
there had been here and there a man, such as Leuwenhoek or
Malpighi, gifted with exceptional vision, and perhaps unusually
happy in his conjectures, who made important contributions to the
knowledge of the minute structure of organic tissues; but now of
a sudden it became possible for the veriest tyro to confirm or
refute the laborious observations of these pioneers, while the
skilled observer could step easily beyond the barriers of vision
that hitherto were quite impassable. And so, naturally enough,
the physiologists of the fourth decade of the nineteenth century
rushed as eagerly into the new realm of the microscope as, for
example, their successors of to-day are exploring the realm of
the X-ray.

Lister himself, who had become an eager interrogator of the
instrument he had perfected, made many important discoveries, the
most notable being his final settlement of the long-mooted
question as to the true form of the red corpuscles of the human
blood. In reality, as everybody knows nowadays, these are
biconcave disks, but owing to their peculiar figure it is easily
possible to misinterpret the appearances they present when seen
through a poor lens, and though Dr. Thomas Young and various
other observers had come very near the truth regarding them,
unanimity of opinion was possible only after the verdict of the
perfected microscope was given.

These blood corpuscles are so infinitesimal in size that
something like five millions of them are found in each cubic
millimetre of the blood, yet they are isolated particles, each
having, so to speak, its own personality.  This, of course, had
been known to microscopists since the days of the earliest
lenses. It had been noticed, too, by here and there an observer,
that certain of the solid tissues seemed to present something of
a granular texture, as if they, too, in their ultimate
constitution, were made up of particles.  And now, as better and
better lenses were constructed, this idea gained ground
constantly, though for a time no one saw its full significance.
In the case of vegetable tissues, indeed, the fact that little
particles encased a membranous covering, and called cells, are
the ultimate visible units of structure had long been known. But
it was supposed that animal tissues differed radically from this
construction.  The elementary particles of vegetables "were
regarded to a certain extent as individuals which composed the
entire plant, while, on the other hand, no such view was taken of
the elementary parts of animals."


ROBERT BROWN AND THE CELL NUCLEUS

In the year 1833 a further insight into the nature of the
ultimate particles of plants was gained through the observation
of the English microscopist Robert Brown, who, in the course of
his microscopic studies of the epidermis of orchids, discovered
in the cells "an opaque spot," which he named the nucleus. 
Doubtless the same "spot" had been seen often enough before by
other observers, but Brown was the first to recognize it as a
component part of the vegetable cell and to give it a name.


"I shall conclude my observations on Orchideae," said Brown,
"with a notice of some points of their general structure, which
chiefly relate to the cellular tissue.  In each cell of the
epidermis of a great part of this family, especially of those
with membranous leaves, a single circular areola, generally
somewhat more opaque than, the membrane of the cell, is
observable. This areola, which is more or less distinctly
granular, is slightly convex, and although it seems to be on the
surface is in reality covered by the outer lamina of the cell.
There is no regularity as to its place in the cell; it is not
unfrequently, however, central or nearly so.

"As only one areola belongs to each cell, and as in many cases
where it exists in the common cells of the epidermis, it is also
visible in the cutaneous glands or stomata, and in these is
always double--one being on each side of the limb--it is highly
probable that the cutaneous gland is in all cases composed of two
cells of peculiar form, the line of union being the longitudinal
axis of the disk or pore.

"This areola, or nucleus of the cell as perhaps it might be
termed, is not confined to the epidermis, being also found, not
only in the pubescence of the surface, particularly when jointed,
as in cypripedium, but in many cases in the parenchyma or
internal cells of the tissue, especially when these are free from
the deposition of granular matter.

"In the compressed cells of the epidermis the nucleus is in a
corresponding degree flattened; but in the internal tissue it is
often nearly spherical, more or less firmly adhering to one of
the walls, and projecting into the cavity of the cell.  In this
state it may not unfrequently be found. in the substance of the
column and in that of the perianthium.

"The nucleus is manifest also in the tissue of the stigma, where
in accordance with the compression of the utriculi, it has an
intermediate form, being neither so much flattened as in the
epidermis nor so convex as it is in the internal tissue of the
column.

"I may here remark that I am acquainted with one case of apparent
exception to the nucleus being solitary in each utriculus or
cell--namely, in Bletia Tankervilliae.  In the utriculi of the
stigma of this plant, I have generally, though not always, found
a second areola apparently on the surface, and composed of much
larger granules than the ordinary nucleus, which is formed of
very minute granular matter, and seems to be deep seated.

"Mr. Bauer has represented the tissue of the stigma, in the
species of Bletia, both before and, as he believes, after
impregnation; and in the latter state the utriculi are marked
with from one to three areolae of similar appearance.

"The nucleus may even be supposed to exist in the pollen of this
family. In the early stages of its formation, at least a minute
areola is of ten visible in the simple grain, and in each of the
constituent parts of cells of the compound grain.  But these
areolae may perhaps rather be considered as merely the points of
production of the tubes.

"This nucleus of the cell is not confined to orchideae, but is
equally manifest in many other monocotyledonous families; and I
have even found it, hitherto however in very few cases, in the
epidermis of dicotyledonous plants; though in this primary
division it may perhaps be said to exist in the early stages of
development of the pollen. Among monocotyledons, the orders in
which it is most remarkable are Liliaceae, Hemerocallideae,
Asphodeleae, Irideae, and Commelineae.

"In some plants belonging to this last-mentioned family,
especially in Tradascantia virginica, and several nearly related
species, it is uncommonly distinct, not in the epidermis and in
the jointed hairs of the filaments, but in the tissue of the
stigma, in the cells of the ovulum even before impregnation, and
in all the stages of formation of the grains of pollen, the
evolution of which is so remarkable in tradascantia.

"The few indications of the presence of this nucleus, or areola,
that I have hitherto met with in the publications of botanists
are chiefly in some figures of epidermis, in the recent works of
Meyen and Purkinje, and in one case, in M. Adolphe Broigniart's
memoir on the structure of leaves.  But so little importance
seems to be attached to it that the appearance is not always
referred to in the explanations of the figures in which it is
represented. Mr. Bauer, however, who has also figured it in the
utriculi of the stigma of Bletia Tankervilliae has more
particularly noticed it, and seems to consider it as only visible
after impregnation."[2]


SCHLEIDEN AND SCHWANN AND THE CELL THEORY

That this newly recognized structure must be important in the
economy of the cell was recognized by Brown himself, and by the
celebrated German Meyen, who dealt with it in his work on
vegetable physiology, published not long afterwards; but it
remained for another German, the professor of botany in the
University of Jena, Dr. M. J. Schleiden, to bring the nucleus to
popular attention, and to assert its all-importance in the
economy of the cell.

Schleiden freely acknowledged his indebtedness to Brown for first
knowledge of the nucleus, but he soon carried his studies of that
structure far beyond those of its discoverer. He came to believe
that the nucleus is really the most important portion of the
cell, in that it is the original structure from which the
remainder of the cell is developed. Hence he named it the
cytoblast.  He outlined his views in an epochal paper published
in Muller's Archives in 1838, under title of "Beitrage zur
Phytogenesis."  This paper is in itself of value, yet the most
important outgrowth of Schleiden's observations of the nucleus
did not spring from his own labors, but from those of a friend to
whom he mentioned his discoveries the year previous to their
publication. This friend was Dr. Theodor Schwann, professor of
physiology in the University of Louvain.

At the moment when these observations were communicated to him
Schwann was puzzling over certain details of animal histology
which he could not clearly explain.  His great teacher, Johannes
Muller, had called attention to the strange resemblance to
vegetable cells shown by certain cells of the chorda dorsalis
(the embryonic cord from which the spinal column is developed),
and Schwann himself had discovered a corresponding similarity in
the branchial cartilage of a tadpole.  Then, too, the researches
of Friedrich Henle had shown that the particles that make up the
epidermis of animals are very cell-like in appearance. Indeed,
the cell-like character of certain animal tissues had come to be
matter of common note among students of minute anatomy. Schwann
felt that this similarity could not be mere coincidence, but he
had gained no clew to further insight until Schleiden called his
attention to the nucleus.  Then at once he reasoned that if there
really is the correspondence between vegetable and animal tissues
that he suspected, and if the nucleus is so important in the
vegetable cell as Schleiden believed, the nucleus should also be
found in the ultimate particles of animal tissues.

Schwann's researches soon showed the entire correctness of this
assumption. A closer study of animal tissues under the microscope
showed, particularly in the case of embryonic tissues, that
"opaque spots" such as Schleiden described are really to be found
there in abundance--forming, indeed, a most characteristic phase
of the structure. The location of these nuclei at comparatively
regular intervals suggested that they are found in definite
compartments of the tissue, as Schleiden had shown to be the case
with vegetables; indeed, the walls that separated such cell-like
compartments one from another were in some cases visible.
Particularly was this found to be the case with embryonic
tissues, and the study of these soon convinced Schwann that his
original surmise had been correct, and that all animal tissues
are in their incipiency composed of particles not unlike the
ultimate particles of vegetables in short, of what the botanists
termed cells.  Adopting this name, Schwann propounded what soon
became famous as his cell theory, under title of Mikroskopische
Untersuchungen uber die Ubereinstimmung in der Structur und dent
Wachsthum der Thiere und Pflanzen.  So expeditious had been his
work that this book was published early in 1839, only a few
months after the appearance of Schleiden's paper.

As the title suggests, the main idea that actuated Schwann was to
unify vegetable and animal tissues. Accepting cell-structure as
the basis of all vegetable tissues, he sought to show that the
same is true of animal tissues, all the seeming diversities of
fibre being but the alteration and development of what were
originally simple cells. And by cell Schwann meant, as did
Schleiden also, what the word ordinarily implies--a cavity walled
in on all sides. He conceived that the ultimate constituents of
all tissues were really such minute cavities, the most important
part of which was the cell wall, with its associated nucleus. He
knew, indeed, that the cell might be filled with fluid contents,
but he regarded these as relatively subordinate in importance to
the wall itself.  This, however, did not apply to the nucleus,
which was supposed to lie against the cell wall and in the
beginning to generate it.  Subsequently the wall might grow so
rapidly as to dissociate itself from its contents, thus becoming
a hollow bubble or true cell; but the nucleus, as long as it
lasted, was supposed to continue in contact with the cell wall.
Schleiden had even supposed the nucleus to be a constituent part
of the wall, sometimes lying enclosed between two layers of its
substance, and Schwann quoted this view with seeming approval.
Schwann believed, however, that in the mature cell the nucleus
ceased to be functional and disappeared.

The main thesis as to the similarity of development of vegetable
and animal tissues and the cellular nature of the ultimate
constitution of both was supported by a mass of carefully
gathered evidence which a multitude of microscopists at once
confirmed, so Schwann's work became a classic almost from the
moment of its publication. Of course various other workers at
once disputed Schwann's claim to priority of discovery, in
particular the English microscopist Valentin, who asserted, not
without some show of justice, that he was working closely along
the same lines.  Put so, for that matter, were numerous others,
as Henle, Turpin, Du-mortier, Purkinje, and Muller, all of whom
Schwann himself had quoted.  Moreover, there were various
physiologists who earlier than any of these had foreshadowed the
cell theory--notably Kaspar Friedrich Wolff, towards the close of
the previous century, and Treviranus about 1807, But, as we have
seen in so many other departments of science, it is one thing to
foreshadow a discovery, it is quite another to give it full
expression and make it germinal of other discoveries. And when
Schwann put forward the explicit claim that "there is one
universal principle of development for the elementary parts, of
organisms, however different, and this principle is the formation
of cells," he enunciated a doctrine which was for all practical
purposes absolutely new and opened up a novel field for the
microscopist to enter. A most important era in physiology dates
from the publication of his book in 1839.


THE CELL THEORY ELABORATED

That Schwann should have gone to embryonic tissues for the
establishment of his ideas was no doubt due very largely to the
influence of the great Russian Karl Ernst von Baer, who about ten
years earlier had published the first part of his celebrated work
on embryology, and whose ideas were rapidly gaining ground,
thanks largely to the advocacy of a few men, notably Johannes
Muller, in Germany, and William B. Carpenter, in England, and to
the fact that the improved microscope had made minute anatomy
popular.  Schwann's researches made it plain that the best field
for the study of the animal cell is here, and a host of explorers
entered the field. The result of their observations was, in the
main, to confirm the claims of Schwann as to the universal
prevalence of the cell. The long-current idea that animal tissues
grow only as a sort of deposit from the blood-vessels was now
discarded, and the fact of so-called plantlike growth of animal
cells, for which Schwann contended, was universally accepted. Yet
the full measure of the affinity between the two classes of cells
was not for some time generally apprehended.

Indeed, since the substance that composes the cell walls of
plants is manifestly very different from the limiting membrane of
the animal cell, it was natural, so long as the, wall was
considered the most essential part of the structure, that the
divergence between the two classes of cells should seem very
pronounced.  And for a time this was the conception of the matter
that was uniformly accepted. But as time went on many observers
had their attention called to the peculiar characteristics of the
contents of the cell, and were led to ask themselves whether
these might not be more important than had been supposed.  In
particular, Dr. Hugo von Mohl, professor of botany in the
University of Tubingen, in the course of his exhaustive studies
of the vegetable cell, was impressed with the peculiar and
characteristic appearance of the cell contents. He observed
universally within the cell "an opaque, viscid fluid, having
granules intermingled in it," which made up the main substance of
the cell, and which particularly impressed him because under
certain conditions it could be seen to be actively in motion, its
parts separated into filamentous streams.

Von Mohl called attention to the fact that this motion of the
cell contents had been observed as long ago as 1774 by
Bonaventura Corti, and rediscovered in 1807 by Treviranus, and
that these observers had described the phenomenon under the "most
unsuitable name of 'rotation of the cell sap.' Von Mohl
recognized that the streaming substance was something quite
different from sap. He asserted that the nucleus of the cell lies
within this substance and not attached to the cell wall as
Schleiden had contended. He saw, too, that the chlorophyl
granules, and all other of the cell contents, are incorporated
with the "opaque, viscid fluid," and in 1846 he had become so
impressed with the importance of this universal cell substance
that be gave it the name of protoplasm. Yet in so doing he had no
intention of subordinating the cell wall. The fact that Payen, in
1844, had demonstrated that the cell walls of all vegetables,
high or low, are composed largely of one substance, cellulose,
tended to strengthen the position of the cell wall as the really
essential structure, of which the protoplasmic contents were only
subsidiary products.

Meantime, however, the students of animal histology were more and
more impressed with the seeming preponderance of cell contents
over cell walls in the tissues they studied.  They, too, found
the cell to be filled with a viscid, slimy fluid capable of
motion. To this Dujardin gave the name of sarcode.  Presently it
came to be known, through the labors of Kolliker, Nageli,
Bischoff, and various others, that there are numerous lower forms
of animal life which seem to be composed of this sarcode, without
any cell wall whatever. The same thing seemed to be true of
certain cells of higher organisms, as the blood corpuscles. 
Particularly in the case of cells that change their shape
markedly, moving about in consequence of the streaming of their
sarcode, did it seem certain that no cell wall is present, or
that, if present, its role must be insignificant.

And so histologists came to question whether, after all, the cell
contents rather than the enclosing wall must not be the really
essential structure, and the weight of increasing observations
finally left no escape from the conclusion that such is really
the case. But attention being thus focalized on the cell
contents, it was at once apparent that there is a far closer
similarity between the ultimate particles of vegetables and those
of animals than had been supposed. Cellulose and animal membrane
being now regarded as more by-products, the way was clear for the
recognition of the fact that vegetable protoplasm and animal
sarcode are marvellously similar in appearance and general
properties. The closer the observation the more striking seemed
this similarity; and finally, about 1860, it was demonstrated by
Heinrich de Bary and by Max Schultze that the two are to all
intents and purposes identical. Even earlier Remak had reached a
similar conclusion, and applied Von Mohl's word protoplasm to
animal cell contents, and now this application soon became
universal.  Thenceforth this protoplasm was to assume the utmost
importance in the physiological world, being recognized as the
universal "physical basis of life," vegetable and animal alike.
This amounted to the logical extension and culmination of
Schwann's doctrine as to the similarity of development of the two
animate kingdoms. Yet at the, same time it was in effect the
banishment of the cell that Schwann had defined.  The word cell
was retained, it is true, but it no longer signified a minute
cavity.  It now implied, as Schultze defined it, "a small mass of
protoplasm endowed with the attributes of life." This definition
was destined presently to meet with yet another modification, as
we shall see; but the conception of the protoplasmic mass as the
essential ultimate structure, which might or might not surround
itself with a protective covering, was a permanent addition to
physiological knowledge. The earlier idea had, in effect,
declared the shell the most important part of the egg; this
developed view assigned to the yolk its true position.

In one other important regard the theory of Schleiden and Schwann
now became modified.  This referred to the origin of the cell.
Schwann had regarded cell growth as a kind of crystallization,
beginning with the deposit of a nucleus about a granule in the
intercellular substance--the cytoblastema, as Schleiden called
it. But Von Mohl, as early as 1835, had called attention to the
formation of new vegetable cells through the division of a
pre-existing cell. Ehrenberg, another high authority of the time,
contended that no such division occurs, and the matter was still
in dispute when Schleiden came forward with his discovery of
so-called free cell-formation within the parent cell, and this
for a long time diverted attention from the process of division
which Von Mohl had described. All manner of schemes of
cell-formation were put forward during the ensuing years by a
multitude of observers, and gained currency notwithstanding Von
Mohl's reiterated contention that there are really but two ways
in which the formation of new cells takes place--namely, "first,
through division of older cells; secondly, through the formation
of secondary cells lying free in the cavity of a cell."

But gradually the researches of such accurate observers as Unger,
Nageli, Kolliker, Reichart, and Remak tended to confirm the
opinion of Von Mohl that cells spring only from cells, and
finally Rudolf Virchow brought the matter to demonstration about
1860.  His Omnis cellula e cellula became from that time one of
the accepted data of physiology. This was supplemented a little
later by Fleming's Omnis nucleus e nucleo, when still more
refined methods of observation had shown that the part of the
cell which always first undergoes change preparatory to new
cell-formation is the all-essential nucleus. Thus the nucleus was
restored to the important position which Schwann and Schleiden
had given it, but with greatly altered significance.  Instead of
being a structure generated de novo from non-cellular substance,
and disappearing as soon as its function of cell-formation was
accomplished, the nucleus was now known as the central and
permanent feature of every cell, indestructible while the cell
lives, itself the division-product of a pre-existing nucleus, and
the parent, by division of its substance, of other generations of
nuclei. The word cell received a final definition as "a small
mass of protoplasm supplied with a nucleus."

In this widened and culminating general view of the cell theory
it became clear that every animate organism, animal or vegetable,
is but a cluster of nucleated cells, all of which, in each
individual case, are the direct descendants of a single
primordial cell of the ovum. In the developed individuals of
higher organisms the successive generations of cells become
marvellously diversified in form and in specific functions; there
is a wonderful division of labor, special functions being chiefly
relegated to definite groups of cells; but from first to last
there is no function developed that is not present, in a
primitive way, in every cell, however isolated; nor does the
developed cell, however specialized, ever forget altogether any
one of its primordial functions or capacities. All physiology,
then, properly interpreted, becomes merely a study of cellular
activities; and the development of the cell theory takes its
place as the great central generalization in physiology of the
nineteenth century.  Something of the later developments of this
theory we shall see in another connection.


ANIMAL CHEMISTRY

Just at the time when the microscope was opening up the paths
that were to lead to the wonderful cell theory, another novel
line of interrogation of the living organism was being put
forward by a different set of observers. Two great schools of
physiological chemistry had arisen--one under guidance of Liebig
and Wohler, in Germany, the other dominated by the great French
master Jean Baptiste Dumas.  Liebig had at one time contemplated
the study of medicine, and Dumas had achieved distinction in
connection with Prevost, at Geneva, in the field of pure
physiology before he turned his attention especially to
chemistry.  Both these masters, therefore, and Wohler as well,
found absorbing interest in those phases of chemistry that have
to do with the functions of living tissues; and it was largely
through their efforts and the labors of their followers that the
prevalent idea that vital processes are dominated by unique laws
was discarded and physiology was brought within the recognized
province of the chemist. So at about the time when the microscope
had taught that the cell is the really essential structure of the
living organism, the chemists had come to understand that every
function of the organism is really the expression of a chemical
change--that each cell is, in short, a miniature chemical
laboratory. And it was this combined point of view of anatomist
and chemist, this union of hitherto dissociated forces, that made
possible the inroads into the unexplored fields of physiology
that were effected towards the middle of the nineteenth century.

One of the first subjects reinvestigated and brought to proximal
solution was the long-mooted question of the digestion of foods.
Spallanzani and Hunter had shown in the previous century that
digestion is in some sort a solution of foods; but little advance
was made upon their work until 1824, when Prout detected the
presence of hydrochloric acid in the gastric juice. A decade
later Sprott and Boyd detected the existence of peculiar glands
in the gastric mucous membrane; and Cagniard la Tour and Schwann
independently discovered that the really active principle of the
gastric juice is a substance which was named pepsin, and which
was shown by Schwann to be active in the presence of hydrochloric
acid.

Almost coincidently, in 1836, it was discovered by Purkinje and
Pappenheim that another organ than the stomach--namely, the
pancreas--has a share in digestion, and in the course of the
ensuing decade it came to be known, through the efforts of
Eberle, Valentin, and Claude Bernard, that this organ is
all-important in the digestion of starchy and fatty foods. It was
found, too, that the liver and the intestinal glands have each an
important share in the work of preparing foods for absorption, as
also has the saliva--that, in short, a coalition of forces is
necessary for the digestion of all ordinary foods taken into the
stomach.

And the chemists soon discovered that in each one of the
essential digestive juices there is at least one substance having
certain resemblances to pepsin, though acting on different kinds
of food.  The point of resemblance between all these essential
digestive agents is that each has the remarkable property of
acting on relatively enormous quantities of the substance which
it can digest without itself being destroyed or apparently even
altered. In virtue of this strange property, pepsin and the
allied substances were spoken of as ferments, but more recently
it is customary to distinguish them from such organized ferments
as yeast by designating them enzymes. The isolation of these
enzymes, and an appreciation of their mode of action, mark a long
step towards the solution of the riddle of digestion, but it must
be added that we are still quite in the dark as to the real
ultimate nature of their strange activity.

In a comprehensive view, the digestive organs, taken as a whole,
are a gateway between the outside world and the more intimate
cells of the organism.  Another equally important gateway is
furnished by the lungs, and here also there was much obscurity
about the exact method of functioning at the time of the revival
of physiological chemistry. That oxygen is consumed and carbonic
acid given off during respiration the chemists of the age of
Priestley and Lavoisier had indeed made clear, but the mistaken
notion prevailed that it was in the lungs themselves that the
important burning of fuel occurs, of which carbonic acid is a
chief product.  But now that attention had been called to the
importance of the ultimate cell, this misconception could not
long hold its ground, and as early as 1842 Liebig, in the course
of his studies of animal heat, became convinced that it is not in
the lungs, but in the ultimate tissues to which they are
tributary, that the true consumption of fuel takes place.
Reviving Lavoisier's idea, with modifications and additions,
Liebig contended, and in the face of opposition finally
demonstrated, that the source of animal heat is really the
consumption of the fuel taken in through the stomach and the
lungs.  He showed that all the activities of life are really the
product of energy liberated solely through destructive processes,
amounting, broadly speaking, to combustion occurring in the
ultimate cells of the organism. Here is his argument:


LIEBIG ON ANIMAL HEAT

"The oxygen taken into the system is taken out again in the same
forms, whether in summer or in winter; hence we expire more
carbon in cold weather, and when the barometer is high, than we
do in warm weather; and we must consume more or less carbon in
our food in the same proportion; in Sweden more than in Sicily;
and in our more temperate climate a full eighth more in winter
than in summer.

"Even when we consume equal weights of food in cold and warm
countries, infinite wisdom has so arranged that the articles of
food in different climates are most unequal in the proportion of
carbon they contain. The fruits on which the natives of the South
prefer to feed do not in the fresh state contain more than twelve
per cent. of carbon, while the blubber and train-oil used by the
inhabitants of the arctic regions contain from sixty-six to
eighty per cent. of carbon.

"It is no difficult matter, in warm climates, to study moderation
in eating, and men can bear hunger for a long time under the
equator; but cold and hunger united very soon exhaust the body.

"The mutual action between the elements of the food and the
oxygen conveyed by the circulation of the blood to every part of
the body is the source of animal heat.

"All living creatures whose existence depends on the absorption
of oxygen possess within themselves a source of heat independent
of surrounding objects.

"This truth applies to all animals, and extends besides to the
germination of seeds, to the flowering of plants, and to the
maturation of fruits. It is only in those parts of the body to
which arterial blood, and with it the oxygen absorbed in
respiration, is conveyed that heat is produced. Hair, wool, or
feathers do not possess an elevated temperature. This high
temperature of the animal body, or, as it may be called,
disengagement of heat, is uniformly and under all circumstances
the result of the combination of combustible substance with
oxygen.

"In whatever way carbon may combine with oxygen, the act of
combination cannot take place without the disengagement of heat.
It is a matter of indifference whether the combination takes
place rapidly or slowly, at a high or at a low temperature; the
amount of heat liberated is a constant quantity. The carbon of
the food, which is converted into carbonic acid within the body,
must give out exactly as much heat as if it had been directly
burned in the air or in oxygen gas; the only difference is that
the amount of heat produced is diffused over unequal times. In
oxygen the combustion is more rapid and the heat more intense; in
air it is slower, the temperature is not so high, but it
continues longer.

"It is obvious that the amount of heat liberated must increase or
diminish with the amount of oxygen introduced in equal times by
respiration. Those animals which respire frequently, and
consequently consume much oxygen, possess a higher temperature
than others which, with a body of equal size to be heated, take
into the system less oxygen. The temperature of a child (102
degrees) is higher than that of an adult (99.5 degrees). That of
birds (104 to 105.4 degrees) is higher than that of quadrupeds
(98.5 to 100.4 degrees), or than that of fishes or amphibia,
whose proper temperature is from 3.7 to 2.6 degrees higher than
that of the medium in which they live.  All animals, strictly
speaking, are warm-blooded; but in those only which possess lungs
is the temperature of the body independent of the surrounding
medium.

"The most trustworthy observations prove that in all climates, in
the temperate zones as well as at the equator or the poles, the
temperature of the body in man, and of what are commonly called
warm-blooded animals, is invariably the same; yet how different
are the circumstances in which they live.

"The animal body is a heated mass, which bears the same relation
to surrounding objects as any other heated mass. It receives heat
when the surrounding objects are hotter, it loses heat when they
are colder than itself.  We know that the rapidity of cooling
increases with the difference between the heated body and that of
the surrounding medium--that is, the colder the surrounding
medium the shorter the time required for the cooling of the
heated body. How unequal, then, must be the loss of heat of a man
at Palermo, where the actual temperature is nearly equal to that
of the body, and in the polar regions, where the external
temperature is from 70 to 90 degrees lower.

"Yet notwithstanding this extremely unequal loss of heat,
experience has shown that the blood of an inhabitant of the
arctic circle has a temperature as high as that of the native of
the South, who lives in so different a medium.  This fact, when
its true significance is perceived, proves that the heat given
off to the surrounding medium is restored within the body with
great rapidity. This compensation takes place more rapidly in
winter than in summer, at the pole than at the equator.

"Now in different climates the quantity of oxygen introduced into
the system of respiration, as has been already shown, varies
according to the temperature of the external air; the quantity of
inspired oxygen increases with the loss of heat by external
cooling, and the quantity of carbon or hydrogen necessary to
combine with this oxygen must be increased in like ratio. It is
evident that the supply of heat lost by cooling is effected by
the mutual action of the elements of the food and the inspired
oxygen, which combine together.  To make use of a familiar, but
not on that account a less just illustration, the animal body
acts, in this respect, as a furnace, which we supply with fuel.
It signifies nothing what intermediate forms food may assume,
what changes it may undergo in the body, the last change is
uniformly the conversion of carbon into carbonic acid and of its
hydrogen into water; the unassimilated nitrogen of the food,
along with the unburned or unoxidized carbon, is expelled in the
excretions. In order to keep up in a furnace a constant
temperature, we must vary the supply of fuel according to the
external temperature--that is, according to the supply of oxygen.

"In the animal body the food is the fuel; with a proper supply of
oxygen we obtain the heat given out during its oxidation or
combustion."[3]


BLOOD CORPUSCLES, MUSCLES, AND GLANDS

Further researches showed that the carriers of oxygen, from the
time of its absorption in the lungs till its liberation in the
ultimate tissues, are the red corpuscles, whose function had been
supposed to be the mechanical one of mixing of the blood.  It
transpired that the red corpuscles are composed chiefly of a
substance which Kuhne first isolated in crystalline form in 1865,
and which was named haemoglobin--a substance which has a
marvellous affinity for oxygen, seizing on it eagerly at the
lungs vet giving it up with equal readiness when coursing among
the remote cells of the body. When freighted with oxygen it
becomes oxyhaemoglobin and is red in color; when freed from its
oxygen it takes a purple hue; hence the widely different
appearance of arterial and venous blood, which so puzzled the
early physiologists.

This proof of the vitally important role played by the red-blood
corpuscles led, naturally, to renewed studies of these
infinitesimal bodies. It was found that they may vary greatly in
number at different periods in the life of the same individual,
proving that they may be both developed and destroyed in the
adult organism.  Indeed, extended observations left no reason to
doubt that the process of corpuscle formation and destruction may
be a perfectly normal one--that, in short, every red-blood
corpuscle runs its course and dies like any more elaborate
organism. They are formed constantly in the red marrow of bones,
and are destroyed in the liver, where they contribute to the
formation of the coloring matter of the bile.  Whether there are
other seats of such manufacture and destruction of the corpuscles
is not yet fully determined. Nor are histologists agreed as to
whether the red-blood corpuscles themselves are to be regarded as
true cells, or merely as fragments of cells budded out from a
true cell for a special purpose; but in either case there is not
the slightest doubt that the chief function of the red corpuscle
is to carry oxygen.

If the oxygen is taken to the ultimate cells before combining
with the combustibles it is to consume, it goes without saying
that these combustibles themselves must be carried there also.
Nor could it be in doubt that the chiefest of these ultimate
tissues, as regards, quantity of fuel required, are the muscles.
A general and comprehensive view of the organism includes, then,
digestive apparatus and lungs as the channels of fuel-supply;
blood and lymph channels as the transportation system; and muscle
cells, united into muscle fibres, as the consumption furnaces,
where fuel is burned and energy transformed and rendered
available for the purposes of the organism, supplemented by a set
of excretory organs, through which the waste products--the
ashes--are eliminated from the system.

But there remain, broadly speaking, two other sets of organs
whose size demonstrates their importance in the economy of the
organism, yet whose functions are not accounted for in this
synopsis. These are those glandlike organs, such as the spleen,
which have no ducts and produce no visible secretions, and the
nervous mechanism, whose central organs are the brain and spinal
cord.  What offices do these sets of organs perform in the great
labor-specializing aggregation of cells which we call a living
organism?

As regards the ductless glands, the first clew to their function
was given when the great Frenchman Claude Bernard (the man of
whom his admirers loved to say, "He is not a physiologist merely;
he is physiology itself") discovered what is spoken of as the
glycogenic function of the liver. The liver itself, indeed, is
not a ductless organ, but the quantity of its biliary output
seems utterly disproportionate to its enormous size, particularly
when it is considered that in the case of the human species the
liver contains normally about one-fifth of all the blood in the
entire body. Bernard discovered that the blood undergoes a change
of composition in passing through the liver.  The liver cells
(the peculiar forms of which had been described by Purkinje,
Henle, and Dutrochet about 1838) have the power to convert
certain of the substances that come to them into a starchlike
compound called glycogen, and to store this substance away till
it is needed by the organism.  This capacity of the liver cells
is quite independent of the bile-making power of the same cells;
hence the discovery of this glycogenic function showed that an
organ may have more than one pronounced and important specific
function. But its chief importance was in giving a clew to those
intermediate processes between digestion and final assimilation
that are now known to be of such vital significance in the
economy of the organism.

In the forty odd years that have elapsed since this pioneer
observation of Bernard, numerous facts have come to light showing
the extreme importance of such intermediate alterations of
food-supplies in the blood as that performed by the liver. It has
been shown that the pancreas, the spleen, the thyroid gland, the
suprarenal capsules are absolutely essential, each in its own
way, to the health of the organism, through metabolic changes
which they alone seem capable of performing; and it is suspected
that various other tissues, including even the muscles
themselves, have somewhat similar metabolic capacities in
addition to their recognized functions. But so extremely
intricate is the chemistry of the substances involved that in no
single case has the exact nature of the metabolisms wrought by
these organs been fully made out.  Each is in its way a chemical
laboratory indispensable to the right conduct of the organism,
but the precise nature of its operations remains inscrutable. The
vast importance of the operations of these intermediate organs is
unquestioned.

A consideration of the functions of that other set of organs
known collectively as the nervous system is reserved for a later
chapter.



VI. THEORIES OF ORGANIC EVOLUTION

GOETHE AND THE METAMORPHOSIS OF PARTS

When Coleridge said of Humphry Davy that he might have been the
greatest poet of his time had he not chosen rather to be the
greatest chemist, it is possible that the enthusiasm of the
friend outweighed the caution of the critic.  But however that
may be, it is beyond dispute that the man who actually was the
greatest poet of that time might easily have taken the very
highest rank as a scientist had not the muse distracted his
attention.  Indeed, despite these distractions, Johann Wolfgang
von Goethe achieved successes in the field of pure science that
would insure permanent recognition for his name had he never
written a stanza of poetry. Such is the versatility that marks
the highest genius.

It was in 1790 that Goethe published the work that laid the
foundations of his scientific reputation--the work on the
Metamorphoses of Plants, in which he advanced the novel doctrine
that all parts of the flower are modified or metamorphosed
leaves.

"Every one who observes the growth of plants, even
superficially," wrote Goethe, "will notice that certain external
parts of them become transformed at times and go over into the
forms of the contiguous parts, now completely, now to a greater
or less degree.  Thus, for example, the single flower is
transformed into a double one when, instead of stamens, petals
are developed, which are either exactly like the other petals of
the corolla in form, and color or else still bear visible signs
of their origin.

"When we observe that it is possible for a plant in this way to
take a step backward, we shall give so much the more heed to the
regular course of nature and learn the laws of transformation
according to which she produces one part through another, and
displays the most varying forms through the modification of one
single organ.

"Let us first direct our attention to the plant at the moment
when it develops out of the seed-kernel. The first organs of its
upward growth are known by the name of cotyledons; they have also
been called seed-leaves.

"They often appear shapeless, filled with new matter, and are
just as thick as they are broad.  Their vessels are
unrecognizable and are hardly to be distinguished from the mass
of the whole; they bear almost no resemblance to a leaf, and we
could easily be misled into regarding them as special organs. 
Occasionally, however, they appear as real leaves, their vessels
are capable of the most minute development, their similarity to
the following leaves does not permit us to take them for special
organs, but we recognize them instead to be the first leaves of
the stalk.

"The cotyledons are mostly double, and there is an observation to
be made here which will appear still more important as we
proceed--that is, that the leaves of the first node are often
paired, even when the following leaves of the stalk stand
alternately upon it. Here we see an approximation and a joining
of parts which nature afterwards separates and places at a
distance from one another. It is still more remarkable when the
cotyledons take the form of many little leaves gathered about an
axis, and the stalk which grows gradually from their midst
produces the following leaves arranged around it singly in a
whorl. This may be observed very exactly in the growth of the
pinus species. Here a corolla of needles forms at the same time a
calyx, and we shall have occasion to remember the present case in
connection with similar phenomena later.

"On the other hand, we observe that even the cotyledons which are
most like a leaf when compared with the following leaves of the
stalk are always more undeveloped or less developed. This is
chiefly noticeable in their margin which is extremely simple and
shows few traces of indentation.

"A few or many of the next following leaves are often already
present in the seed, and lie enclosed between the cotyledons; in
their folded state they are known by the name of plumules. Their
form, as compared with the cotyledons and the following leaves,
varies in different plants.  Their chief point of variance,
however, from the cotyledons is that they are flat, delicate, and
formed like real leaves generally. They are wholly green, rest on
a visible node, and can no longer deny their relationship to the
following leaves of the stalk, to which, however, they are
usually still inferior, in so far as that their margin is not
completely developed.

"The further development, however, goes on ceaselessly in the
leaf, from node to node; its midrib is elongated, and more or
less additional ribs stretch out from this towards the sides. The
leaves now appear notched, deeply indented, or composed of
several small leaves, in which last case they seem to form
complete little branches.  The date-palm furnishes a striking
example of such a successive transformation of the simplest leaf
form. A midrib is elongated through a succession of several
leaves, the single fan-shaped leaf becomes torn and diverted, and
a very complicated leaf is developed, which rivals a branch in
form.

"The transition to inflorescence takes place more or less
rapidly. In the latter case we usually observe that the leaves of
the stalk loose their different external divisions, and, on the
other hand, spread out more or less in their lower parts where
they are attached to the stalk. If the transition takes place
rapidly, the stalk, suddenly become thinner and more elongated
since the node of the last-developed leaf, shoots up and collects
several leaves around an axis at its end.

"That the petals of the calyx are precisely the same organs which
have hitherto appeared as leaves on the stalk, but now stand
grouped about a common centre in an often very different form,
can, as it seems to me, be most clearly demonstrated.  Already in
connection with the cotyledons above, we noticed a similar
working of nature. The first species, while they are developing
out of the seed-kernel, display a radiate crown of unmistakable
needles; and in the first childhood of these plants we see
already indicated that force of nature whereby when they are
older their flowering and fruit-giving state will be produced.

"We see this force of nature, which collects several leaves
around an axis, produce a still closer union and make these
approximated, modified leaves still more unrecognizable by
joining them together either wholly or partially.  The
bell-shaped or so-called one-petalled calices represent these
cloudy connected leaves, which, being more or less indented from
above, or divided, plainly show their origin.

"We can observe the transition from the calyx to the corolla in
more than one instance, for, although the color of the calyx is
still usually green, and like the color of the leaves of the
stalk, it nevertheless often varies in one or another of its
parts--at the tips, the margins, the back, or even, the inward
side--while the outer still remains on green.

"The relationship of the corolla to the leaves of the stalk is
shown in more than one way, since on the stalks of some plants
appear leaves which are already more or less colored long before
they approach inflorescence; others are fully colored when near
inflorescence.  Nature also goes over at once to the corolla,
sometimes by skipping over the organs of the calyx, and in such a
case we likewise have an opportunity to observe that leaves of
the stalk become transformed into petals. Thus on the stalk of
tulips, for instance, there sometimes appears an almost
completely developed and colored petal. Even more remarkable is
the case when such a leaf, half green and half of it belonging to
the stalk, remains attached to the latter, while another colored
part is raised with the corolla, and the leaf is thus torn in
two.

"The relationship between the petals and stamens is very close.
In some instances nature makes the transition regular--e.g.,
among the Canna and several plants of the same family.  A true,
little-modified petal is drawn together on its upper margin, and
produces a pollen sac, while the rest of the petal takes the
place of the stamen. In double flowers we can observe this
transition in all its stages. In several kinds of roses, within
the fully developed and colored petals there appear other ones
which are drawn together in the middle or on the side.  This
drawing together is produced by a small weal, which appears as a
more or less complete pollen sac, and in the same proportion the
leaf approaches the simple form of a stamen.

"The pistil in many cases looks almost like a stamen without
anthers, and the relationship between the formation of the two is
much closer than between the other parts.  In retrograde fashion
nature often produces cases where the style and stigma (Narben)
become retransformed into petals--that is, the Ranunculus
Asiaticus becomes double by transforming the stigma and style of
the fruit-receptacle into real petals, while the stamens are
often found unchanged immediately behind the corolla.

"In the seed receptacles, in spite of their formation, of their
special object, and of their method of being joined together, we
cannot fail to recognize the leaf form.  Thus, for instance, the
pod would be a simple leaf folded and grown together on its
margin; the siliqua would consist of more leaves folded over
another; the compound receptacles would be explained as being
several leaves which, being united above one centre, keep their
inward parts separate and are joined on their margins. We can
convince ourselves of this by actual sight when such composite
capsules fall apart after becoming ripe, because then every part
displays an opened pod."[1]


The theory thus elaborated of the metamorphosis of parts was
presently given greater generality through extension to the
animal kingdom, in the doctrine which Goethe and Oken advanced
independently, that the vertebrate skull is essentially a
modified and developed vertebra. These were conceptions worthy of
a poet--impossible, indeed, for any mind that had not the poetic
faculty of correlation.  But in this case the poet's vision was
prophetic of a future view of the most prosaic science. The
doctrine of metamorphosis of parts soon came to be regarded as of
fundamental importance.

But the doctrine had implications that few of its early advocates
realized. If all the parts of a flower--sepal, petal, stamen,
pistil, with their countless deviations of contour and color--are
but modifications of the leaf, such modification implies a
marvellous differentiation and development. To assert that a
stamen is a metamorphosed leaf means, if it means anything, that
in the long sweep of time the leaf has by slow or sudden
gradations changed its character through successive generations,
until the offspring, so to speak, of a true leaf has become a
stamen.  But if such a metamorphosis as this is possible--if the
seemingly wide gap between leaf and stamen may be spanned by the
modification of a line of organisms--where does the possibility
of modification of organic type find its bounds?  Why may not the
modification of parts go on along devious lines until the remote
descendants of an organism are utterly unlike that organism?  Why
may we not thus account for the development of various species of
beings all sprung from one parent stock?  That, too, is a poet's
dream; but is it only a dream? Goethe thought not.  Out of his
studies of metamorphosis of parts there grew in his mind the
belief that the multitudinous species of plants and animals about
us have been evolved from fewer and fewer earlier parent types,
like twigs of a giant tree drawing their nurture from the same
primal root. It was a bold and revolutionary thought, and the
world regarded it as but the vagary of a poet.


ERASMUS DARWIN

Just at the time when this thought was taking form in Goethe's
brain, the same idea was germinating in the mind of another
philosopher, an Englishman of international fame, Dr. Erasmus
Darwin, who, while he lived, enjoyed the widest popularity as a
poet, the rhymed couplets of his Botanic Garden being quoted
everywhere with admiration. And posterity repudiating the verse
which makes the body of the book, yet grants permanent value to
the book itself, because, forsooth, its copious explanatory
foot-notes furnish an outline of the status of almost every
department of science of the time.

But even though he lacked the highest art of the versifier,
Darwin had, beyond peradventure, the imagination of a poet
coupled with profound scientific knowledge; and it was his poetic
insight, correlating organisms seemingly diverse in structure and
imbuing the lowliest flower with a vital personality, which led
him to suspect that there are no lines of demarcation in nature.
"Can it be," he queries, "that one form of organism has developed
from another; that different species are really but modified
descendants of one parent stock?"  The alluring thought nestled
in his mind and was nurtured there, and grew in a fixed belief,
which was given fuller expression in his Zoonomia and in the
posthumous Temple of Nature.

Here is his rendering of the idea as versified in the Temple of
Nature:

 "Organic life beneath the shoreless waves
  Was born, and nursed in Ocean's pearly caves;
  First forms minute, unseen by spheric glass,
  Move on the mud, or pierce the watery mass;
  These, as successive generations bloom,
  New powers acquire and larger limbs assume;
  Whence countless groups of vegetation spring,
  And breathing realms of fin, and feet, and wing.

 "Thus the tall Oak, the giant of the wood,
  Which bears Britannia's thunders on the flood;
  The Whale, unmeasured monster of the main;
  The lordly lion, monarch of the plain;
  The eagle, soaring in the realms of air,
  Whose eye, undazzled, drinks the solar glare;
  Imperious man, who rules the bestial crowd,
  Of language, reason, and reflection proud,
  With brow erect, who scorns this earthy sod,
  And styles himself the image of his God--
  Arose from rudiments of form and sense,
  An embryon point or microscopic ens!"[2]


Here, clearly enough, is the idea of evolution.  But in that day
there was little proof forthcoming of its validity that could
satisfy any one but a poet, and when Erasmus Darwin died, in
1802, the idea of transmutation of species was still but an
unsubstantiated dream.

It was a dream, however, which was not confined to Goethe and
Darwin. Even earlier the idea had come more or less vaguely to
another great dreamer--and worker--of Germany, Immanuel Kant, and
to several great Frenchmen, including De Maillet, Maupertuis,
Robinet, and the famous naturalist Buffon--a man who had the
imagination of a poet, though his message was couched in most
artistic prose.  Not long after the middle of the eighteenth
century Buffon had put forward the idea of transmutation of
species, and he reiterated it from time to time from then on till
his death in 1788. But the time was not yet ripe for the idea of
transmutation of species to burst its bonds.

And yet this idea, in a modified or undeveloped form, had taken
strange hold upon the generation that was upon the scene at the
close of the eighteenth century. Vast numbers of hitherto unknown
species of animals had been recently discovered in previously
unexplored regions of the globe, and the wise men were sorely
puzzled to account for the disposal of all of these at the time
of the deluge.  It simplified matters greatly to suppose that
many existing species had been developed since the episode of the
ark by modification of the original pairs. The remoter bearings
of such a theory were overlooked for the time, and the idea that
American animals and birds, for example, were modified
descendants of Old-World forms--the jaguar of the leopard, the
puma of the lion, and so on--became a current belief with that
class of humanity who accept almost any statement as true that
harmonizes with their prejudices without realizing its
implications.

Thus it is recorded with eclat that the discovery of the close
proximity of America at the northwest with Asia removes all
difficulties as to the origin of the Occidental faunas and
floras, since Oriental species might easily have found their way
to America on the ice, and have been modified as we find them by
"the well-known influence of climate." And the persons who gave
expression to this idea never dreamed of its real significance. 
In truth, here was the doctrine of evolution in a nutshell, and,
because its ultimate bearings were not clear, it seemed the most
natural of doctrines.  But most of the persons who advanced it
would have turned from it aghast could they have realized its
import. As it was, however, only here and there a man like Buffon
reasoned far enough to inquire what might be the limits of such
assumed transmutation; and only here and there a Darwin or a
Goethe reached the conviction that there are no limits.


LAMARCK VERSUS CUVIER

And even Goethe and Darwin had scarcely passed beyond that
tentative stage of conviction in which they held the thought of
transmutation of species as an ancillary belief not ready for
full exposition. There was one of their contemporaries, however,
who, holding the same conception, was moved to give it full
explication. This was the friend and disciple of Buffon, Jean
Baptiste de Lamarck.  Possessed of the spirit of a poet and
philosopher, this great Frenchman had also the widest range of
technical knowledge, covering the entire field of animate nature. 
The first half of his long life was devoted chiefly to botany, in
which he attained high distinction.  Then, just at the beginning
of the nineteenth century, he turned to zoology, in particular to
the lower forms of animal life. Studying these lowly organisms,
existing and fossil, he was more and more impressed with the
gradations of form everywhere to be seen; the linking of diverse
families through intermediate ones; and in particular with the
predominance of low types of life in the earlier geological
strata.  Called upon constantly to classify the various forms of
life in the course of his systematic writings, he found it more
and more difficult to draw sharp lines of demarcation, and at
last the suspicion long harbored grew into a settled conviction
that there is really no such thing as a species of organism in
nature; that "species" is a figment of the human imagination,
whereas in nature there are only individuals.

That certain sets of individuals are more like one another than
like other sets is of course patent, but this only means, said
Lamarck, that these similar groups have had comparatively recent
common ancestors, while dissimilar sets of beings are more
remotely related in consanguinity.  But trace back the lines of
descent far enough, and all will culminate in one original stock. 
All forms of life whatsoever are modified descendants of an
original organism. From lowest to highest, then, there is but one
race, one species, just as all the multitudinous branches and
twigs from one root are but one tree. For purposes of convenience
of description, we may divide organisms into orders, families,
genera, species, just as we divide a tree into root, trunk,
branches, twigs, leaves; but in the one case, as in the other,
the division is arbitrary and artificial.

In Philosophie Zoologique (1809), Lamarck first explicitly
formulated his ideas as to the transmutation of species, though
he had outlined them as early as 1801.  In this memorable
publication not only did he state his belief more explicitly and
in fuller detail than the idea had been expressed by any
predecessor, but he took another long forward step, carrying him
far beyond all his forerunners except Darwin, in that he made an
attempt to explain the way in which the transmutation of species
had been brought about. The changes have been wrought, he said,
through the unceasing efforts of each organism to meet the needs
imposed upon it by its environment. Constant striving means the
constant use of certain organs. Thus a bird running by the
seashore is constantly tempted to wade deeper and deeper in
pursuit of food; its incessant efforts tend to develop its legs,
in accordance with the observed principle that the use of any
organ tends to strengthen and develop it. But such slightly
increased development of the legs is transmitted to the off
spring of the bird, which in turn develops its already improved
legs by its individual efforts, and transmits the improved
tendency. Generation after generation this is repeated, until the
sum of the infinitesimal variations, all in the same direction,
results in the production of the long-legged wading-bird. In a
similar way, through individual effort and transmitted tendency,
all the diversified organs of all creatures have been
developed--the fin of the fish, the wing of the bird, the hand of
man; nay, more, the fish itself, the bird, the man, even. 
Collectively the organs make up the entire organism; and what is
true of the individual organs must be true also of their
ensemble, the living being.

Whatever might be thought of Lamarck's explanation of the cause
of transmutation--which really was that already suggested by
Erasmus Darwin--the idea of the evolution for which he contended
was but the logical extension of the conception that American
animals are the modified and degenerated descendants of European
animals. But people as a rule are little prone to follow ideas to
their logical conclusions, and in this case the conclusions were
so utterly opposed to the proximal bearings of the idea that the
whole thinking world repudiated them with acclaim. The very
persons who had most eagerly accepted the idea of transmutation
of European species into American species, and similar limited
variations through changed environment, because of the relief
thus given the otherwise overcrowded ark, were now foremost in
denouncing such an extension of the doctrine of transmutation as
Lamarck proposed.

And, for that matter, the leaders of the scientific world were
equally antagonistic to the Lamarckian hypothesis.  Cuvier in
particular, once the pupil of Lamarck, but now his colleague, and
in authority more than his peer, stood out against the
transmutation doctrine with all his force. He argued for the
absolute fixity of species, bringing to bear the resources of a
mind which, as a mere repository of facts, perhaps never was
excelled. As a final and tangible proof of his position, he
brought forward the bodies of ibises that had been embalmed by
the ancient Egyptians, and showed by comparison that these do not
differ in the slightest particular from the ibises that visit the
Nile to-day.

Cuvier's reasoning has such great historical interest--being the
argument of the greatest opponent of evolution of that day--that
we quote it at some length.

"The following objections," he says, "have already been started
against my conclusions.  Why may not the presently existing races
of mammiferous land quadrupeds be mere modifications or varieties
of those ancient races which we now find in the fossil state,
which modifications may have been produced by change of climate
and other local circumstances, and since raised to the present
excessive difference by the operations of similar causes during a
long period of ages?

"This objection may appear strong to those who believe in the
indefinite possibility of change of form in organized bodies, and
think that, during a succession of ages and by alterations of
habitudes, all the species may change into one another, or one of
them give birth to all the rest. Yet to these persons the
following answer may be given from their own system: If the
species have changed by degrees, as they assume, we ought to find
traces of this gradual modification.  Thus, between the
palaeotherium and the species of our own day, we should be able
to discover some intermediate forms; and yet no such discovery
has ever been made. Since the bowels of the earth have not
preserved monuments of this strange genealogy, we have no right
to conclude that the ancient and now extinct species were as
permanent in their forms and characters as those which exist at
present; or, at least, that the catastrophe which destroyed them
did not leave sufficient time for the productions of the changes
that are alleged to have taken place.

"In order to reply to those naturalists who acknowledge that the
varieties of animals are restrained by nature within certain
limits, it would be necessary to examine how far these limits
extend. This is a very curious inquiry, and in itself exceedingly
interesting under a variety of relations, but has been hitherto
very little attended to. . . . . . . . .

Wild animals which subsist upon herbage feel the influence of
climate a little more extensively, because there is added to it
the influence of food, both in regard to its abundance and its
quality. Thus the elephants of one forest are larger than those
of another; their tusks also grow somewhat longer in places where
their food may happen to be more favorable for the production of
the substance of ivory. The same may take place in regard to the
horns of stags and reindeer. But let us examine two elephants,
the most dissimilar that can be conceived, we shall not discover
the smallest difference in the number and articulations of the
bones, the structure of the teeth, etc. . . . . . . . .

"Nature appears also to have guarded against the alterations of
species which might proceed from mixture of breeds by influencing
the various species of animals with mutual aversion from one
another. Hence all the cunning and all the force that man is able
to exert is necessary to accomplish such unions, even between
species that have the nearest resemblances.  And when the mule
breeds that are thus produced by these forced conjunctions happen
to be fruitful, which is seldom the case, this fecundity never
continues beyond a few generations, and would not probably
proceed so far without a continuance of the same cares which
excited it at first. Thus we never see in a wild state
intermediate productions between the hare and the rabbit, between
the stag and the doe, or between the marten and the weasel.  But
the power of man changes this established order, and continues to
produce all these intermixtures of which the various species are
susceptible, but which they would never produce if left to
themselves.

"The degrees of these variations are proportional to the
intensity of the causes that produced them--namely, the slavery
or subjection under which those animals are to man. They do not
proceed far in half-domesticated species. In the cat, for
example, a softer or harsher fur, more brilliant or more varied
colors, greater or less size--these form the whole extent of
variety in the species; the skeleton of the cat of Angora differs
in no regular and constant circumstances from the wild-cat of
Europe. . . . . . . .

The most remarkable effects of the influence of man are produced
upon that animal which he has reduced most completely under
subjection. Dogs have been transported by mankind into every part
of the world and have submitted their action to his entire
direction. Regulated in their unions by the pleasure or caprice
of their masters, the almost endless varieties of dogs differ
from one another in color, in length, and abundance of hair,
which is sometimes entirely wanting; in their natural instincts;
in size, which varies in measure as one to five, mounting in some
instances to more than a hundredfold in bulk; in the form of
their ears, noses, and tails; in the relative length of their
legs; in the progressive development of the brain, in several of
the domesticated varieties occasioning alterations even in the
form of the head, some of them having long, slender muzzles with
a flat forehead, others having short muzzles with a forehead
convex, etc., insomuch that the apparent difference between a
mastiff and a water-spaniel and between a greyhound and a pugdog
are even more striking than between almost any of the wild
species of a genus. . . . . . . .

It follows from these observations that animals have certain
fixed and natural characters which resist the effects of every
kind of influence, whether proceeding from natural causes or
human interference; and we have not the smallest reason to
suspect that time has any more effect on them than climate.

"I am aware that some naturalists lay prodigious stress upon the
thousands which they can call into action by a dash of their
pens. In such matters, however, our only way of judging as to the
effects which may be produced by a long period of time is by
multiplying, as it were, such as are produced by a shorter time. 
With this view I have endeavored to collect all the ancient
documents respecting the forms of animals; and there are none
equal to those furnished by the Egyptians, both in regard to
their antiquity and abundance. They have not only left us
representatives of animals, but even their identical bodies
embalmed and preserved in the catacombs.

"I have examined, with the greatest attention, the engraved
figures of quadrupeds and birds brought from Egypt to ancient
Rome, and all these figures, one with another, have a perfect
resemblance to their intended objects, such as they still are
to-day.

"From all these established facts, there does not seem to be the
smallest foundation for supposing that the new genera which I
have discovered or established among extraneous fossils, such as
the paleoetherium, anoplotherium, megalonyx, mastodon,
pterodactylis, etc., have ever been the sources of any of our
present animals, which only differ so far as they are influenced
by time or climate. Even if it should prove true, which I am far
from believing to be the case, that the fossil elephants,
rhinoceroses, elks, and bears do not differ further from the
existing species of the same genera than the present races of
dogs differ among themselves, this would by no means be a
sufficient reason to conclude that they were of the same species;
since the races or varieties of dogs have been influenced by the
trammels of domesticity, which those other animals never did, and
indeed never could, experience."[3]


To Cuvier's argument from the fixity of Egyptian mummified birds
and animals, as above stated, Lamarck replied that this proved
nothing except that the ibis had become perfectly adapted to its
Egyptian surroundings in an early day, historically speaking, and
that the climatic and other conditions of the Nile Valley had not
since then changed. His theory, he alleged, provided for the
stability of species under fixed conditions quite as well as for
transmutation under varying conditions.

But, needless to say, the popular verdict lay with Cuvier; talent
won for the time against genius, and Lamarck was looked upon as
an impious visionary.  His faith never wavered, however. He
believed that he had gained a true insight into the processes of
animate nature, and he reiterated his hypotheses over and over,
particularly in the introduction to his Histoire Naturelle des
Animaux sans Vertebres, in 1815, and in his Systeme des
Connaissances Positives de l'Homme, in 1820. He lived on till
1829, respected as a naturalist, but almost unrecognized as a
prophet.


TENTATIVE ADVANCES

While the names of Darwin and Goethe, and in particular that of
Lamarck, must always stand out in high relief in this generation
as the exponents of the idea of transmutation of species, there
are a few others which must not be altogether overlooked in this
connection.  Of these the most conspicuous is that of Gottfried
Reinhold Treviranus, a German naturalist physician, professor of
mathematics in the lyceum at Bremen.

It was an interesting coincidence that Treviranus should have
published the first volume of his Biologie, oder Philosophie der
lebenden Natur, in which his views on the transmutation of
species were expounded, in 1802, the same twelvemonth in which
Lamarck's first exposition of the same doctrine appeared in his
Recherches sur l'Organisation des Corps Vivants.  It is singular,
too, that Lamarck, in his Hydrogelogie of the same date, should
independently have suggested "biology" as an appropriate word to
express the general science of living things. It is significant
of the tendency of thought of the time that the need of such a
unifying word should have presented itself simultaneously to
independent thinkers in different countries.

That same memorable year, Lorenz Oken, another philosophical
naturalist, professor in the University of Zurich, published the
preliminary outlines of his Philosophie der Natur, which, as
developed through later publications, outlined a theory of
spontaneous generation and of evolution of species. Thus it
appears that this idea was germinating in the minds of several of
the ablest men of the time during the first decade of our
century. But the singular result of their various explications
was to give sudden check to that undercurrent of thought which
for some time had been setting towards this conception.  As soon
as it was made clear whither the concession that animals may be
changed by their environment must logically trend, the recoil
from the idea was instantaneous and fervid. Then for a generation
Cuvier was almost absolutely dominant, and his verdict was
generally considered final.

There was, indeed, one naturalist of authority in France who had
the hardihood to stand out against Cuvier and his school, and who
was in a position to gain a hearing, though by no means to divide
the following. This was Etienne Geoffroy Saint-Hilaire, the
famous author of the Philosophie Anatomique, and for many years
the colleague of Lamarck at the Jardin des Plantes.  Like Goethe,
Geoffroy was pre-eminently an anatomist, and, like the great
German, he had early been impressed with the resemblances between
the analogous organs of different classes of beings.  He
conceived the idea that an absolute unity of type prevails
throughout organic nature as regards each set of organs. Out of
this idea grew his gradually formed belief that similarity of
structure might imply identity of origin--that, in short, one
species of animal might have developed from another.

Geoffroy's grasp of this idea of transmutation was by no means so
complete as that of Lamarck, and he seems never to have fully
determined in his own mind just what might be the limits of such
development of species. Certainly he nowhere includes all organic
creatures in one line of descent, as Lamarck had done;
nevertheless, he held tenaciously to the truth as he saw it, in
open opposition to Cuvier, with whom he held a memorable debate
at the Academy of Sciences in 1830--the debate which so aroused
the interest and enthusiasm of Goethe, but which, in the opinion
of nearly every one else, resulted in crushing defeat for
Geoffrey, and brilliant, seemingly final, victory for the
advocate of special creation and the fixity of species.

With that all ardent controversy over the subject seemed to end,
and for just a quarter of a century to come there was published
but a single argument for transmutation of species which
attracted any general attention whatever.  This oasis in a desert
generation was a little book called Vestiges of the Natural
History of Creation, which appeared anonymously in England in
1844, and which passed through numerous editions, and was the
subject of no end of abusive and derisive comment. This book, the
authorship of which remained for forty years a secret, is now
conceded to have been the work of Robert Chambers, the well-known
English author and publisher.  The book itself is remarkable as
being an avowed and unequivocal exposition of a general doctrine
of evolution, its view being as radical and comprehensive as that
of Lamarck himself. But it was a resume of earlier efforts rather
than a new departure, to say nothing of its technical
shortcomings, which may best be illustrated by a quotation.

"The whole question," says Chambers, "stands thus:  For the
theory of universal order--that is, order as presiding in both
the origin and administration of the world--we have the testimony
of a vast number of facts in nature, and this one in
addition--that whatever is left from the domain of ignorance, and
made undoubted matter of science, forms a new support to the same
doctrine.  The opposite view, once predominant, has been
shrinking for ages into lesser space, and now maintains a footing
only in a few departments of nature which happen to be less
liable than others to a clear investigation. The chief of these,
if not almost the only one, is the origin of the organic
kingdoms.  So long as this remains obscure, the supernatural will
have a certain hold upon enlightened persons. Should it ever be
cleared up in a way that leaves no doubt of a natural origin of
plants and animals, there must be a complete revolution in the
view which is generally taken of the relation of the Father of
our being.

"This prepares the way for a few remarks on the present state of
opinion with regard to the origin of organic nature. The great
difficulty here is the apparent determinateness of species. These
forms of life being apparently unchangeable, or at least always
showing a tendency to return to the character from which they
have diverged, the idea arises that there can have been no
progression from one to another; each must have taken its special
form, independently of other forms, directly from the appointment
of the Creator.  The Edinburgh Review writer says, 'they were
created by the hand of God and adapted to the conditions of the
period.' Now it is, in the first place, not certain that species
constantly maintain a fixed character, for we have seen that what
were long considered as determinate species have been transmuted
into others. Passing, however, from this fact, as it is not
generally received among men of science, there remain some great
difficulties in connection with the idea of special creation. 
First we should have to suppose, as pointed out in my former
volume, a most startling diversity of plan in the divine
workings, a great general plan or system of law in the leading
events of world-making, and a plan of minute, nice operation, and
special attention in some of the mere details of the process. The
discrepancy between the two conceptions is surely overpowering,
when we allow ourselves to see the whole matter in a steady and
rational light. There is, also, the striking fact of an
ascertained historical progress of plants and animals in the
order of their organization; marine and cellular plants and
invertebrated animals first, afterwards higher examples of both. 
In an arbitrary system we had surely no reason to expect mammals
after reptiles; yet in this order they came. The writer in the
Edinburgh Review speaks of animals as coming in adaptation to
conditions, but this is only true in a limited sense. The groves
which formed the coal-beds might have been a fitting habitation
for reptiles, birds, and mammals, as such groves are at the
present day; yet we see none of the last of these classes and
hardly any traces of the two first at that period of the earth. 
Where the iguanodon lived the elephant might have lived, but
there was no elephant at that time. The sea of the Lower Silurian
era was capable of supporting fish, but no fish existed.  It
hence forcibly appears that theatres of life must have remained
unserviceable, or in the possession of a tenantry inferior to
what might have enjoyed them, for many ages: there surely would
have been no such waste allowed in a system where Omnipotence was
working upon the plan of minute attention to specialities. The
fact seems to denote that the actual procedure of the peopling of
the earth was one of a natural kind, requiring a long space of
time for its evolution.  In this supposition the long existence
of land without land animals, and more particularly without the
noblest classes and orders, is only analogous to the fact, not
nearly enough present to the minds of a civilized people, that to
this day the bulk of the earth is a waste as far as man is
concerned.

"Another startling objection is in the infinite local variation
of organic forms.  Did the vegetable and animal kingdoms consist
of a definite number of species adapted to peculiarities of soil
and climate, and universally distributed, the fact would be in
harmony with the idea of special exertion.  But the truth is that
various regions exhibit variations altogether without apparent
end or purpose.  Professor Henslow enumerates forty-five distinct
flowers or sets of plants upon the surface of the earth,
notwithstanding that many of these would be equally suitable
elsewhere. The animals of different continents are equally
various, few species being the same in any two, though the
general character may conform. The inference at present drawn
from this fact is that there must have been, to use the language
of the Rev. Dr. Pye Smith, 'separate and original creations,
perhaps at different and respectively distinct epochs.' It seems
hardly conceivable that rational men should give an adherence to
such a doctrine when we think of what it involves. In the single
fact that it necessitates a special fiat of the inconceivable
Author of this sand-cloud of worlds to produce the flora of St.
Helena, we read its more than sufficient condemnation. It surely
harmonizes far better with our general ideas of nature to suppose
that, just as all else in this far-spread science was formed on
the laws impressed upon it at first by its Author, so also was
this. An exception presented to us in such a light appears
admissible only when we succeed in forbidding our minds to follow
out those reasoning processes to which, by another law of the
Almighty, they tend, and for which they are adapted."[4]


Such reasoning as this naturally aroused bitter animadversions,
and cannot have been without effect in creating an undercurrent
of thought in opposition to the main trend of opinion of the
time. But the book can hardly be said to have done more than
that. Indeed, some critics have denied it even this merit. After
its publication, as before, the conception of transmutation of
species remained in the popular estimation, both lay and
scientific, an almost forgotten "heresy."

It is true that here and there a scientist of greater or less
repute--as Von Buch, Meckel, and Von Baer in Germany, Bory
Saint-Vincent in France, Wells, Grant, and Matthew in England,
and Leidy in America--had expressed more or less tentative
dissent from the doctrine of special creation and immutability of
species, but their unaggressive suggestions, usually put forward
in obscure publications, and incidentally, were utterly
overlooked and ignored. And so, despite the scientific advances
along many lines at the middle of the century, the idea of the
transmutability of organic races had no such prominence, either
in scientific or unscientific circles, as it had acquired fifty
years before. Special creation held the day, seemingly unopposed.


DARWIN AND THE ORIGIN OF SPECIES

But even at this time the fancied security of the
special-creation hypothesis was by no means real.  Though it
seemed so invincible, its real position was that of an apparently
impregnable fortress beneath which, all unbeknown to the
garrison, a powder-mine has been dug and lies ready for
explosion. For already there existed in the secluded work-room of
an English naturalist, a manuscript volume and a portfolio of
notes which might have sufficed, if given publicity, to shatter
the entire structure of the special-creation hypothesis. The
naturalist who, by dint of long and patient effort, had
constructed this powder-mine of facts was Charles Robert Darwin,
grandson of the author of Zoonomia.

As long ago as July 1, 1837, young Darwin, then twenty-eight
years of age, had opened a private journal, in which he purposed
to record all facts that came to him which seemed to have any
bearing on the moot point of the doctrine of transmutation of
species.  Four or five years earlier, during the course of that
famous trip around the world with Admiral Fitzroy, as naturalist
to the Beagle, Darwin had made the personal observations which
first tended to shake his belief of the fixity of species. In
South America, in the Pampean formation, he had discovered "great
fossil animals covered with armor like that on the existing
armadillos," and had been struck with this similarity of type
between ancient and existing faunas of the same region.  He was
also greatly impressed by the manner in which closely related
species of animals were observed to replace one another as he
proceeded southward over the continent; and "by the
South-American character of most of the productions of the
Galapagos Archipelago, and more especially by the manner in which
they differ slightly on each island of the group, none of the
islands appearing to be very ancient in a geological sense."

At first the full force of these observations did not strike him;
for, under sway of Lyell's geological conceptions, he tentatively
explained the relative absence of life on one of the Galapagos
Islands by suggesting that perhaps no species had been created
since that island arose. But gradually it dawned upon him that
such facts as he had observed "could only be explained on the
supposition that species gradually become modified." From then
on, as he afterwards asserted, the subject haunted him; hence the
journal of 1837.

It will thus be seen that the idea of the variability of species
came to Charles Darwin as an inference from personal observations
in the field, not as a thought borrowed from books.  He had, of
course, read the works of his grandfather much earlier in life,
but the arguments of Zoonomia and The Temple of Nature had not
served in the least to weaken his acceptance of the current
belief in fixity of species. Nor had he been more impressed with
the doctrine of Lamarck, so closely similar to that of his
grandfather.  Indeed, even after his South-American experience
had aroused him to a new point of view he was still unable to see
anything of value in these earlier attempts at an explanation of
the variation of species. In opening his journal, therefore, he
had no preconceived notion of upholding the views of these or any
other makers of hypotheses, nor at the time had he formulated any
hypothesis of his own. His mind was open and receptive; he was
eager only for facts which might lead him to an understanding of
a problem which seemed utterly obscure. It was something to feel
sure that species have varied; but how have such variations been
brought about?

It was not long before Darwin found a clew which he thought might
lead to the answer he sought.  In casting about for facts he had
soon discovered that the most available field for observation lay
among domesticated animals, whose numerous variations within
specific lines are familiar to every one.  Thus under
domestication creatures so tangibly different as a mastiff and a
terrier have sprung from a common stock. So have the Shetland
pony, the thoroughbred, and the draught-horse. In short, there is
no domesticated animal that has not developed varieties deviating
more or less widely from the parent stock. Now, how has this been
accomplished?  Why, clearly, by the preservation, through
selective breeding, of seemingly accidental variations. Thus one
horseman, by constantly selecting animals that "chance" to have
the right build and stamina, finally develops a race of
running-horses; while another horseman, by selecting a different
series of progenitors, has developed a race of slow, heavy
draught animals.

So far, so good; the preservation of "accidental" variations
through selective breeding is plainly a means by which races may
be developed that are very different from their original parent
form. But this is under man's supervision and direction.  By what
process could such selection be brought about among creatures in
a state of nature? Here surely was a puzzle, and one that must be
solved before another step could be taken in this direction.

The key to the solution of this puzzle came into Darwin's mind
through a chance reading of the famous essay on "Population"
which Thomas Robert Malthus had published almost half a century
before. This essay, expositing ideas by no means exclusively
original with Malthus, emphasizes the fact that organisms tend to
increase at a geometrical ratio through successive generations,
and hence would overpopulate the earth if not somehow kept in
check. Cogitating this thought, Darwin gained a new insight into
the processes of nature.  He saw that in virtue of this tendency
of each race of beings to overpopulate the earth, the entire
organic world, animal and vegetable, must be in a state of
perpetual carnage and strife, individual against individual,
fighting for sustenance and life.

That idea fully imagined, it becomes plain that a selective
influence is all the time at work in nature, since only a few
individuals, relatively, of each generation can come to maturity,
and these few must, naturally, be those best fitted to battle
with the particular circumstances in the midst of which they are
placed. In other words, the individuals best adapted to their
surroundings will, on the average, be those that grow to maturity
and produce offspring. To these offspring will be transmitted the
favorable peculiarities. Thus these peculiarities will become
permanent, and nature will have accomplished precisely what the
human breeder is seen to accomplish. Grant that organisms in a
state of nature vary, however slightly, one from another (which
is indubitable), and that such variations will be transmitted by
a parent to its offspring (which no one then doubted); grant,
further, that there is incessant strife among the various
organisms, so that only a small proportion can come to
maturity--grant these things, said Darwin, and we have an
explanation of the preservation of variations which leads on to
the transmutation of species themselves.

This wonderful coign of vantage Darwin had reached by 1839. Here
was the full outline of his theory; here were the ideas which
afterwards came to be embalmed in familiar speech in the phrases
"spontaneous variation," and the "survival of the fittest,"
through "natural selection."  After such a discovery any ordinary
man would at once have run through the streets of science, so to
speak, screaming "Eureka!"  Not so Darwin.  He placed the
manuscript outline of his theory in his portfolio, and went on
gathering facts bearing on his discovery.  In 1844 he made an
abstract in a manuscript book of the mass of facts by that time
accumulated. He showed it to his friend Hooker, made careful
provision for its publication in the event of his sudden death,
then stored it away in his desk and went ahead with the gathering
of more data. This was the unexploded powder-mine to which I have
just referred.

Twelve years more elapsed--years during which the silent worker
gathered a prodigious mass of facts, answered a multitude of
objections that arose in his own mind, vastly fortified his
theory. All this time the toiler was an invalid, never knowing a
day free from illness and discomfort, obliged to husband his
strength, never able to work more than an hour and a half at a
stretch; yet he accomplished what would have been vast
achievements for half a dozen men of robust health.  Two friends
among the eminent scientists of the day knew of his labors--Sir
Joseph Hooker, the botanist, and Sir Charles Lyell, the
geologist.  Gradually Hooker had come to be more than half a
convert to Darwin's views. Lyell was still sceptical, yet he
urged Darwin to publish his theory without further delay lest he
be forestalled. At last the patient worker decided to comply with
this advice, and in 1856 he set to work to make another and
fuller abstract of the mass of data he had gathered.

And then a strange thing happened.  After Darwin had been at work
on his "abstract" about two years, but before he had published a
line of it, there came to him one day a paper in manuscript, sent
for his approval by a naturalist friend named Alfred Russel
Wallace, who had been for some time at work in the East India
Archipelago.  He read the paper, and, to his amazement, found
that it contained an outline of the same theory of "natural
selection" which he himself had originated and for twenty years
had worked upon. Working independently, on opposite sides of the
globe, Darwin and Wallace had hit upon the same explanation of
the cause of transmutation of species. "Were Wallace's paper an
abstract of my unpublished manuscript of 1844," said Darwin, "it
could not better express my ideas."

Here was a dilemma.  To publish this paper with no word from
Darwin would give Wallace priority, and wrest from Darwin the
credit of a discovery which he had made years before his
codiscoverer entered the field.  Yet, on the other hand, could
Darwin honorably do otherwise than publish his friend's paper and
himself remain silent? It was a complication well calculated to
try a man's soul. Darwin's was equal to the test.  Keenly alive
to the delicacy of the position, he placed the whole matter
before his friends Hooker and Lyell, and left the decision as to
a course of action absolutely to them.  Needless to say, these
great men did the one thing which insured full justice to all
concerned. They counselled a joint publication, to include on the
one hand Wallace's paper, and on the other an abstract of
Darwin's ideas, in the exact form in which it had been outlined
by the author in a letter to Asa Gray in the previous year--an
abstract which was in Gray's hands before Wallace's paper was in
existence. This joint production, together with a full statement
of the facts of the case, was presented to the Linnaean Society
of London by Hooker and Lyell on the evening of July 1, 1858,
this being, by an odd coincidence, the twenty-first anniversary
of the day on which Darwin had opened his journal to collect
facts bearing on the "species question."  Not often before in the
history of science has it happened that a great theory has been
nurtured in its author's brain through infancy and adolescence to
its full legal majority before being sent out into the world.

Thus the fuse that led to the great powder-mine had been lighted.
The explosion itself came more than a year later, in November,
1859, when Darwin, after thirteen months of further effort,
completed the outline of his theory, which was at first begun as
an abstract for the Linnaean Society, but which grew to the size
of an independent volume despite his efforts at condensation, and
which was given that ever-to-be-famous title, The Origin of
Species by Means of Natural Selection, or the Preservation of
Favored Races in the Struggle for Life.  And what an explosion it
was!  The joint paper of 1858 had made a momentary flare, causing
the hearers, as Hooker said, to "speak of it with bated breath,"
but beyond that it made no sensation.  What the result was when
the Origin itself appeared no one of our generation need be told.
The rumble and roar that it made in the intellectual world have
not yet altogether ceased to echo after more than forty years of
reverberation.


NEW CHAMPIONS

To the Origin of Species, then, and to its author, Charles
Darwin, must always be ascribed chief credit for that vast
revolution in the fundamental beliefs of our race which has come
about since 1859, and which made the second half of the century
memorable. But it must not be overlooked that no such sudden
metamorphosis could have been effected had it not been for the
aid of a few notable lieutenants, who rallied to the standards of
the leader immediately after the publication of the Origin. 
Darwin had all along felt the utmost confidence in the ultimate
triumph of his ideas. "Our posterity," he declared, in a letter
to Hooker, "will marvel as much about the current belief [in
special creation] as we do about fossil shells having been
thought to be created as we now see them." But he fully realized
that for the present success of his theory of transmutation the
championship of a few leaders of science was all-essential. He
felt that if he could make converts of Hooker and Lyell and of
Thomas Henry Huxley at once, all would be well.

His success in this regard, as in others, exceeded his
expectations. Hooker was an ardent disciple from reading the
proof-sheets before the book was published; Lyell renounced his
former beliefs and fell into line a few months later; while
Huxley, so soon as he had mastered the central idea of natural
selection, marvelled that so simple yet all-potent a thought had
escaped him so long, and then rushed eagerly into the fray,
wielding the keenest dialectic blade that was drawn during the
entire controversy.  Then, too, unexpected recruits were found in
Sir John Lubbock and John Tyndall, who carried the war eagerly
into their respective territories; while Herbert Spencer, who had
advocated a doctrine of transmutation on philosophic grounds some
years before Darwin published the key to the mystery--and who
himself had barely escaped independent discovery of that
key--lent his masterful influence to the cause. In America the
famous botanist Asa Gray, who had long been a correspondent of
Darwin's but whose advocacy of the new theory had not been
anticipated, became an ardent propagandist; while in Germany
Ernst Heinrich Haeckel, the youthful but already noted zoologist,
took up the fight with equal enthusiasm.

Against these few doughty champions--with here and there another
of less general renown--was arrayed, at the outset, practically
all Christendom.  The interest of the question came home to every
person of intelligence, whatever his calling, and the more deeply
as it became more and more clear how far-reaching are the real
bearings of the doctrine of natural selection. Soon it was seen
that should the doctrine of the survival of the favored races
through the struggle for existence win, there must come with it
as radical a change in man's estimate of his own position as had
come in the day when, through the efforts of Copernicus and
Galileo, the world was dethroned from its supposed central
position in the universe.  The whole conservative majority of
mankind recoiled from this necessity with horror. And this
conservative majority included not laymen merely, but a vast
preponderance of the leaders of science also.

With the open-minded minority, on the other hand, the theory of
natural selection made its way by leaps and bounds. Its
delightful simplicity--which at first sight made it seem neither
new nor important--coupled with the marvellous comprehensiveness
of its implications, gave it a hold on the imagination, and
secured it a hearing where other theories of transmutation of
species had been utterly scorned. Men who had found Lamarck's
conception of change through voluntary effort ridiculous, and the
vaporings of the Vestiges altogether despicable, men whose
scientific cautions held them back from Spencer's deductive
argument, took eager hold of that tangible, ever-present
principle of natural selection, and were led on and on to its
goal.  Hour by hour the attitude of the thinking world towards
this new principle changed; never before was so great a
revolution wrought so suddenly.

Nor was this merely because "the times were ripe" or "men's minds
prepared for evolution."  Darwin himself bears witness that this
was not altogether so.  All through the years in which he brooded
this theory he sounded his scientific friends, and could find
among them not one who acknowledged a doctrine of transmutation.
The reaction from the stand-point of Lamarck and Erasmus Darwin
and Goethe had been complete, and when Charles Darwin avowed his
own conviction he expected always to have it met with ridicule or
contempt. In 1857 there was but one man speaking with any large
degree of authority in the world who openly avowed a belief in
transmutation of species--that man being Herbert Spencer.  But
the Origin of Species came, as Huxley has said, like a flash in
the darkness, enabling the benighted voyager to see the way.  The
score of years during which its author had waited and worked had
been years well spent.  Darwin had become, as he himself says, a
veritable Croesus, "overwhelmed with his riches in facts"--facts
of zoology, of selective artificial breeding, of geographical
distribution of animals, of embryology, of paleontology. He had
massed his facts about his theory, condensed them and
recondensed, until his volume of five hundred pages was an
encyclopaedia in scope. During those long years of musing he had
thought out almost every conceivable objection to his theory, and
in his book every such objection was stated with fullest force
and candor, together with such reply as the facts at command
might dictate. It was the force of those twenty years of effort
of a master-mind that made the sudden breach in the
breaswtork{sic} of current thought.

Once this breach was effected the work of conquest went rapidly
on. Day by day squads of the enemy capitulated and struck their
arms. By the time another score of years had passed the doctrine
of evolution had become the working hypothesis of the scientific
world. The revolution had been effected.

And from amid the wreckage of opinion and belief stands forth the
figure of Charles Darwin, calm, imperturbable, serene; scatheless
to ridicule, contumely, abuse; unspoiled by ultimate success;
unsullied alike by the strife and the victory--take him for all
in all, for character, for intellect, for what he was and what he
did, perhaps the most Socratic figure of the century.  When, in
1882, he died, friend and foe alike conceded that one of the
greatest sons of men had rested from his labors, and all the
world felt it fitting that the remains of Charles Darwin should
be entombed in Westminster Abbey close beside the honored grave
of Isaac Newton.  Nor were there many who would dispute the
justice of Huxley's estimate of his accomplishment: "He found a
great truth trodden under foot.  Reviled by bigots, and ridiculed
by all the world, he lived long enough to see it, chiefly by his
own efforts, irrefragably established in science, inseparably
incorporated with the common thoughts of men, and only hated and
feared by those who would revile but dare not."


THE ORIGIN OF THE FITTEST

Wide as are the implications of the great truth which Darwin and
his co-workers established, however, it leaves quite untouched
the problem of the origin of those "favored variations" upon
which it operates. That such variations are due to fixed and
determinate causes no one understood better than Darwin; but in
his original exposition of his doctrine he made no assumption as
to what these causes are. He accepted the observed fact of
variation--as constantly witnessed, for example, in the
differences between parents and offspring--and went ahead from
this assumption.

But as soon as the validity of the principle of natural selection
came to be acknowledged speculators began to search for the
explanation of those variations which, for purposes of argument,
had been provisionally called "spontaneous." Herbert Spencer had
all along dwelt on this phase of the subject, expounding the
Lamarckian conceptions of the direct influence of the environment
(an idea which had especially appealed to Buffon and to Geoffroy
Saint-Hilaire), and of effort in response to environment and
stimulus as modifying the individual organism, and thus supplying
the basis for the operation of natural selection. Haeckel also
became an advocate of this idea, and presently there arose a
so-called school of neo-Lamarckians, which developed particular
strength and prominence in America under the leadership of
Professors A. Hyatt and E. D. Cope.

But just as the tide of opinion was turning strongly in this
direction, an utterly unexpected obstacle appeared in the form of
the theory of Professor August Weismann, put forward in 1883,
which antagonized the Lamarckian conception (though not touching
the Darwinian, of which Weismann is a firm upholder) by denying
that individual variations, however acquired by the mature
organism, are transmissible. The flurry which this denial created
has not yet altogether subsided, but subsequent observations seem
to show that it was quite disproportionate to the real merits of
the case. Notwithstanding Professor Weismann's objections, the
balance of evidence appears to favor the view that the Lamarckian
factor of acquired variations stands as the complement of the
Darwinian factor of natural selection in effecting the
transmutation of species.

Even though this partial explanation of what Professor Cope calls
the "origin of the fittest" be accepted, there still remains one
great life problem which the doctrine of evolution does not
touch. The origin of species, genera, orders, and classes of
beings through endless transmutations is in a sense explained;
but what of the first term of this long series?  Whence came that
primordial organism whose transmuted descendants make up the
existing faunas and floras of the globe?

There was a time, soon after the doctrine of evolution gained a
hearing, when the answer to that question seemed to some
scientists of authority to have been given by experiment.
Recurring to a former belief, and repeating some earlier
experiments, the director of the Museum of Natural History at
Rouen, M. F. A. Pouchet, reached the conclusion that organic
beings are spontaneously generated about us constantly, in the
familiar processes of putrefaction, which were known to be due to
the agency of microscopic bacteria. But in 1862 Louis Pasteur
proved that this seeming spontaneous generation is in reality due
to the existence of germs in the air. Notwithstanding the
conclusiveness of these experiments, the claims of Pouchet were
revived in England ten years later by Professor Bastian; but then
the experiments of John Tyndall, fully corroborating the results
of Pasteur, gave a final quietus to the claim of "spontaneous
generation" as hitherto formulated.

There for the moment the matter rests.  But the end is not yet.
Fauna and flora are here, and, thanks to Lamarck and Wallace and
Darwin, their development, through the operation of those
"secondary causes" which we call laws of nature, has been
proximally explained. The lowest forms of life have been linked
with the highest in unbroken chains of descent.  Meantime,
through the efforts of chemists and biologists, the gap between
the inorganic and the organic worlds, which once seemed almost
infinite, has been constantly narrowed. Already philosophy can
throw a bridge across that gap. But inductive science, which
builds its own bridges, has not yet spanned the chasm, small
though it appear.  Until it shall have done so, the bridge of
organic evolution is not quite complete; yet even as it stands
to-day it is perhaps the most stupendous scientific structure of
the nineteenth century.



VII. EIGHTEENTH-CENTURY MEDICINE

THE SYSTEM OF BOERHAAVE

At least two pupils of William Harvey distinguished themselves in
medicine, Giorgio Baglivi (1669-1707), who has been called the
"Italian Sydenham," and Hermann Boerhaave (1668-1738). The work
of Baglivi was hardly begun before his early death removed one of
the most promising of the early eighteenth-century physicians. 
Like Boerhaave, he represents a type of skilled, practical
clinitian rather than the abstract scientist. One of his
contributions to medical literature is the first accurate
description of typhoid, or, as he calls it, mesenteric fever.

If for nothing else, Boerhaave must always be remembered as the
teacher of Von Haller, but in his own day he was the widest known
and the most popular teacher in the medical world.  He was the
idol of his pupils at Leyden, who flocked to his lectures in such
numbers that it became necessary to "tear down the walls of
Leyden to accommodate them." His fame extended not only all over
Europe but to Asia, North America, and even into South America. 
A letter sent him from China was addressed to "Boerhaave in
Europe."  His teachings represent the best medical knowledge of
his day, a high standard of morality, and a keen appreciation of
the value of observation; and it was through such teachings
imparted to his pupils and advanced by them, rather than to any
new discoveries, that his name is important in medical history.
His arrangement and classification of the different branches of
medicine are interesting as representing the attitude of the
medical profession towards these various branches at that time.


"In the first place we consider Life; then Health, afterwards
Diseases; and lastly their several Remedies.

"Health the first general branch of Physic in our Institutions is
termed Physiology, or the Animal Oeconomy; demonstrating the
several Parts of the human Body, with their Mechanism and
Actions.

"The second branch of Physic is called Pathology, treating of
Diseases, their Differences, Causes and Effects, or Symptoms; by
which the human Body is known to vary from its healthy state.

"The third part of Physic is termed Semiotica, which shows the
Signs distinguishing between sickness and Health, Diseases and
their Causes in the human Body; it also imports the State and
Degrees of Health and Diseases, and presages their future Events.

"The fourth general branch of Physic is termed Hygiene, or
Prophylaxis.

"The fifth and last part of Physic is called Therapeutica; which
instructs us in the Nature, Preparation and uses of the Materia
Medica; and the methods of applying the same, in order to cure
Diseases and restore lost Health."[1]

From this we may gather that his general view of medicine was not
unlike that taken at the present time.

Boerhaave's doctrines were arranged into a "system" by Friedrich
Hoffmann, of Halle (1660-1742), this system having the merit of
being simple and more easily comprehended than many others.  In
this system forces were considered inherent in matter, being
expressed as mechanical movements, and determined by mass,
number, and weight.  Similarly, forces express themselves in the
body by movement, contraction, and relaxation, etc., and life
itself is movement, "particularly movement of the heart." Life
and death are, therefore, mechanical phenomena, health is
determined by regularly recurring movements, and disease by
irregularity of them. The body is simply a large hydraulic
machine, controlled by "the aether" or "sensitive soul," and the
chief centre of this soul lies in the medulla.

In the practical application of medicines to diseases Hoffman
used simple remedies, frequently with happy results, for whatever
the medical man's theory may be he seldom has the temerity to
follow it out logically, and use the remedies indicated by his
theory to the exclusion of long-established, although perhaps
purely empirical, remedies.  Consequently, many vague theorists
have been excellent practitioners, and Hoffman was one of these.
Some of the remedies he introduced are still in use, notably the
spirits of ether, or "Hoffman's anodyne."


ANIMISTS, VITALISTS, AND ORGANICISTS

Besides Hoffman's system of medicine, there were numerous others
during the eighteenth century, most of which are of no importance
whatever; but three, at least, that came into existence and
disappeared during the century are worthy of fuller notice.  One
of these, the Animists, had for its chief exponent Georg Ernst
Stahl of "phlogiston" fame; another, the Vitalists, was
championed by Paul Joseph Barthez (1734-1806); and the third was
the Organicists.  This last, while agreeing with the other two
that vital activity cannot be explained by the laws of physics
and chemistry, differed in not believing that life "was due to
some spiritual entity," but rather to the structure of the body
itself.

The Animists taught that the soul performed functions of ordinary
life in man, while the life of lower animals was controlled by
ordinary mechanical principles.  Stahl supported this theory
ardently, sometimes violently, at times declaring that there were
"no longer any doctors, only mechanics and chemists." He denied
that chemistry had anything to do with medicine, and, in the
main, discarded anatomy as useless to the medical man. The soul,
he thought, was the source of all vital movement; and the
immediate cause of death was not disease but the direct action of
the soul.  When through some lesion, or because the machinery of
the body has become unworkable, as in old age, the soul leaves
the body and death is produced. The soul ordinarily selects the
channels of the circulation, and the contractile parts, as the
route for influencing the body. Hence in fever the pulse is
quickened, due to the increased activity of the soul, and
convulsions and spasmodic movements in disease are due, to the,
same cause.  Stagnation of the, blood was supposed to be a
fertile cause of diseases, and such diseases were supposed to
arise mostly from "plethora"--an all-important element in Stahl's
therapeutics.  By many this theory is regarded as an attempt on
the part of the pious Stahl to reconcile medicine and theology in
a way satisfactory to both physicians and theologians, but, like
many conciliatory attempts, it was violently opposed by both
doctors and ministers.

A belief in such a theory would lead naturally to simplicity in
therapeutics, and in this respect at least Stahl was consistent.
Since the soul knew more about the body than any physician could
know, Stahl conceived that it would be a hinderance rather than a
help for the physician to interfere with complicated doses of
medicine. As he advanced in age this view of the administration
of drugs grew upon him, until after rejecting quinine, and
finally opium, he at last used only salt and water in treating
his patients. From this last we may judge that his "system," if
not doing much good, was at least doing little harm.

The theory of the Vitalists was closely allied to that of the
Animists, and its most important representative, Paul Joseph
Barthez, was a cultured and eager scientist.  After an eventful
and varied career as physician, soldier, editor, lawyer, and
philosopher in turn, he finally returned to the field of
medicine, was made consulting physician by Napoleon in 1802, and
died in Paris four years later.

The theory that he championed was based on the assumption that
there was a "vital principle," the nature of which was unknown,
but which differed from the thinking mind, and was the cause of
the phenomena of life. This "vital principle" differed from the
soul, and was not exhibited in human beings alone, but even in
animals and plants.  This force, or whatever it might be called,
was supposed to be present everywhere in the body, and all
diseases were the results of it.

The theory of the Organicists, like that of the Animists and
Vitalists, agreed with the other two that vital activity could
not be explained by the laws of physics and chemistry, but,
unlike them, it held that it was a part of the structure of the
body itself. Naturally the practical physicians were more
attracted by this tangible doctrine than by vague theories "which
converted diseases into unknown derangements of some equally
unknown 'principle.' "

It is perhaps straining a point to include this brief description
of these three schools of medicine in the history of the progress
of the science.  But, on the whole, they were negatively at least
prominent factors in directing true progress along its proper
channel, showing what courses were not to be pursued.  Some one
has said that science usually stumbles into the right course only
after stumbling into all the wrong ones; and if this be only
partially true, the wrong ones still play a prominent if not a
very creditable part. Thus the medical systems of William Cullen
(1710-1790), and John Brown (1735-1788), while doing little
towards the actual advancement of scientific medicine, played so
conspicuous a part in so wide a field that the "Brunonian system"
at least must be given some little attention.

According to Brown's theory, life, diseases, and methods of cure
are explained by the property of "excitability."  All exciting
powers were supposed to be stimulating, the apparent debilitating
effects of some being due to a deficiency in the amount of
stimulus. Thus "the whole phenomena of life, health, as well as
disease, were supposed to consist of stimulus and nothing else."
This theory created a great stir in the medical world, and
partisans and opponents sprang up everywhere.  In Italy it was
enthusiastically supported; in England it was strongly opposed;
while in Scotland riots took place between the opposing factions.
Just why this system should have created any stir, either for or
against it, is not now apparent.

Like so many of the other "theorists" of his century, Brown's
practical conclusions deduced from his theory (or perhaps in
spite of it) were generally beneficial to medicine, and some of
them extremely valuable in the treatment of diseases. He first
advocated the modern stimulant, or "feeding treatment" of fevers,
and first recognized the usefulness of animal soups and beef-tea
in certain diseases.


THE SYSTEM OF HAHNEMANN

Just at the close of the century there came into prominence the
school of homoeopathy, which was destined to influence the
practice of medicine very materially and to outlive all the other
eighteenth-century schools. It was founded by Christian Samuel
Friedrich Hahnemann (1755-1843), a most remarkable man, who,
after propounding a theory in his younger days which was at least
as reasonable as most of the existing theories, had the
misfortune to outlive his usefulness and lay his doctrine open to
ridicule by the unreasonable teachings of his dotage,

Hahnemann rejected all the teachings of morbid anatomy and
pathology as useless in practice, and propounded his famous
"similia similibus curantur"--that all diseases were to be cured
by medicine which in health produced symptoms dynamically similar
to the disease under treatment. If a certain medicine produced a
headache when given to a healthy person, then this medicine was
indicated in case of headaches, etc. At the present time such a
theory seems crude enough, but in the latter part of the
eighteenth century almost any theory was as good as the ones
propounded by Animists, Vitalists, and other such schools. It
certainly had the very commendable feature of introducing
simplicity in the use of drugs in place of the complicated
prescriptions then in vogue. Had Hahnemann stopped at this point
he could not have been held up to the indefensible ridicule that
was brought upon him, with considerable justice, by his later
theories.  But he lived onto propound his extraordinary theory of
"potentiality"--that medicines gained strength by being
diluted--and his even more extraordinary theory that all chronic
diseases are caused either by the itch, syphilis, or fig-wart
disease, or are brought on by medicines.

At the time that his theory of potentialities was promulgated,
the medical world had gone mad in its administration of huge
doses of compound mixtures of drugs, and any reaction against
this was surely an improvement.  In short, no medicine at all was
much better than the heaping doses used in common practice; and
hence one advantage, at least, of Hahnemann's methods. Stated
briefly, his theory was that if a tincture be reduced to
one-fiftieth in strength, and this again reduced to one-fiftieth,
and this process repeated up to thirty such dilutions, the
potency of such a medicine will be increased by each dilution,
Hahnemann himself preferring the weakest, or, as he would call
it, the strongest dilution.  The absurdity of such a theory is
apparent when it is understood that long before any drug has been
raised to its thirtieth dilution it has been so reduced in
quantity that it cannot be weighed, measured, or recognized as
being present in the solution at all by any means known to
chemists. It is but just to modern followers of homoeopathy to
say that while most of them advocate small dosage, they do not
necessarily follow the teachings of Hahnemann in this respect,
believing that the theory of the dose "has nothing more to do
with the original law of cure than the psora (itch) theory has;
and that it was one of the later creations of Hahnemann's mind."

Hahnemann's theory that all chronic diseases are derived from
either itch, syphilis, or fig-wart disease is no longer advocated
by his followers, because it is so easily disproved, particularly
in the case of itch. Hahnemann taught that fully three-quarters
of all diseases were caused by "itch struck in," and yet it had
been demonstrated long before his day, and can be demonstrated
any time, that itch is simply a local skin disease caused by a
small parasite.


JENNER AND VACCINATION

All advances in science have a bearing, near or remote, on the
welfare of our race; but it remains to credit to the closing
decade of the eighteenth century a discovery which, in its power
of direct and immediate benefit to humanity, surpasses any other
discovery of this or any previous epoch. Needless to say, I refer
to Jenner's discovery of the method of preventing smallpox by
inoculation with the virus of cow-pox. It detracts nothing from
the merit of this discovery to say that the preventive power of
accidental inoculation had long been rumored among the peasantry
of England.  Such vague, unavailing half-knowledge is often the
forerunner of fruitful discovery.

To all intents and purposes Jenner's discovery was original and
unique. Nor, considered as a perfect method, was it in any sense
an accident. It was a triumph of experimental science.  The
discoverer was no novice in scientific investigation, but a
trained observer, who had served a long apprenticeship in
scientific observation under no less a scientist than the
celebrated John Hunter.  At the age of twenty-one Jenner had gone
to London to pursue his medical studies, and soon after he proved
himself so worthy a pupil that for two years he remained a member
of Hunter's household as his favorite pupil. His taste for
science and natural history soon attracted the attention of Sir
Joseph Banks, who intrusted him with the preparation of the
zoological specimens brought back by Captain Cook's expedition in
1771. He performed this task so well that he was offered the
position of naturalist to the second expedition, but declined it,
preferring to take up the practice of his profession in his
native town of Berkeley.

His many accomplishments and genial personality soon made him a
favorite both as a physician and in society.  He was a good
singer, a fair violinist and flute-player, and a very successful
writer of prose and verse. But with all his professional and
social duties he still kept up his scientific investigations,
among other things making some careful observations on the
hibernation of hedgehogs at the instigation of Hunter, the
results of which were laid before the Royal Society.  He also
made quite extensive investigations as to the geological
formations and fossils found in his neighborhood.

Even during his student days with Hunter he had been much
interested in the belief, current in the rural districts of
Gloucestershire, of the antagonism between cow-pox and small-pox,
a person having suffered from cow-pox being immuned to small-pox.
At various times Jenner had mentioned the subject to Hunter, and
he was constantly making inquiries of his fellow-practitioners as
to their observations and opinions on the subject. Hunter was too
fully engrossed in other pursuits to give the matter much serious
attention, however, and Jenner's brothers of the profession gave
scant credence to the rumors, although such rumors were common
enough.

At this time the practice of inoculation for preventing
small-pox, or rather averting the severer forms of the disease,
was widely practised. It was customary, when there was a mild
case of the disease, to take some of the virus from the patient
and inoculate persons who had never had the disease, producing a
similar attack in them. Unfortunately there were many objections
to this practice. The inoculated patient frequently developed a
virulent form of the disease and died; or if he recovered, even
after a mild attack, he was likely to be "pitted" and disfigured. 
But, perhaps worst of all, a patient so inoculated became the
source of infection to others, and it sometimes happened that
disastrous epidemics were thus brought about.  The case was a
most perplexing one, for the awful scourge of small-pox hung
perpetually over the head of every person who had not already
suffered and recovered from it. The practice of inoculation was
introduced into England by Lady Mary Wortley Montague
(1690-1762), who had seen it practised in the East, and who
announced her intention of "introducing it into England in spite
of the doctors."

From the fact that certain persons, usually milkmaids, who had
suffered from cow-pox seemed to be immuned to small-pox, it would
seem a very simple process of deduction to discover that cow-pox
inoculation was the solution of the problem of preventing the
disease. But there was another form of disease which, while
closely resembling cow-pox and quite generally confounded with
it, did not produce immunity. The confusion of these two forms of
the disease had constantly misled investigations as to the
possibility of either of them immunizing against smallpox, and
the confusion of these two diseases for a time led Jenner to
question the possibility of doing so. After careful
investigations, however, he reached the conclusion that there was
a difference in the effects of the two diseases, only one of
which produced immunity from small-pox.

"There is a disease to which the horse, from his state of
domestication, is frequently subject," wrote Jenner, in his
famous paper on vaccination.  "The farriers call it the grease.
It is an inflammation and swelling in the heel, accompanied at
its commencement with small cracks or fissures, from which issues
a limpid fluid possessing properties of a very peculiar kind.
This fluid seems capable of generating a disease in the human
body (after it has undergone the modification I shall presently
speak of) which bears so strong a resemblance to small-pox that I
think it highly probable it may be the source of that disease.

"In this dairy country a great number of cows are kept, and the
office of milking is performed indiscriminately by men and maid
servants.  One of the former having been appointed to apply
dressings to the heels of a horse affected with the malady I have
mentioned, and not paying due attention to cleanliness,
incautiously bears his part in milking the cows with some
particles of the infectious matter adhering to his fingers. When
this is the case it frequently happens that a disease is
communicated to the cows, and from the cows to the dairy-maids,
which spreads through the farm until most of the cattle and
domestics feel its unpleasant consequences. This disease has
obtained the name of Cow-Pox. It appears on the nipples of the
cows in the form of irregular pustules. At their first appearance
they are commonly of a palish blue, or rather of a color somewhat
approaching to livid, and are surrounded by an inflammation. 
These pustules, unless a timely remedy be applied, frequently
degenerate into phagedenic ulcers, which prove extremely
troublesome.  The animals become indisposed, and the secretion of
milk is much lessened. Inflamed spots now begin to appear on
different parts of the hands of the domestics employed in
milking, and sometimes on the wrists, which run on to
suppuration, first assuming the appearance of the small
vesications produced by a burn. Most commonly they appear about
the joints of the fingers and at their extremities; but whatever
parts are affected, if the situation will admit the superficial
suppurations put on a circular form with their edges more
elevated than their centre and of a color distinctly approaching
to blue. Absorption takes place, and tumors appear in each
axilla. The system becomes affected, the pulse is quickened;
shiverings, succeeded by heat, general lassitude, and pains about
the loins and limbs, with vomiting, come on.  The head is
painful, and the patient is now and then even affected with
delirium. These symptoms, varying in their degrees of violence,
generally continue from one day to three or four, leaving
ulcerated sores about the hands which, from the sensibility of
the parts, are very troublesome and commonly heal slowly,
frequently becoming phagedenic, like those from which they
sprang. During the progress of the disease the lips, nostrils,
eyelids, and other parts of the body are sometimes affected with
sores; but these evidently arise from their being heedlessly
rubbed or scratched by the patient's infected fingers. No
eruptions on the skin have followed the decline of the feverish
symptoms in any instance that has come under my inspection, one
only excepted, and in this case a very few appeared on the arms:
they were very minute, of a vivid red color, and soon died away
without advancing to maturation, so that I cannot determine
whether they had any connection with the preceding symptoms.

"Thus the disease makes its progress from the horse (as I
conceive) to the nipple of the cow, and from the cow to the human
subject.

"Morbid matter of various kinds, when absorbed into the system,
may produce effects in some degree similar; but what renders the
cow-pox virus so extremely singular is that the person that has
been thus affected is forever after secure from the infection of
small-pox, neither exposure to the variolous effluvia nor the
insertion of the matter into the skin producing this
distemper."[2]


In 1796 Jenner made his first inoculation with cowpox matter, and
two months later the same subject was inoculated with small-pox
matter. But, as Jenner had predicted, no attack of small-pox
followed. Although fully convinced by this experiment that the
case was conclusively proven, he continued his investigations,
waiting two years before publishing his discovery. Then,
fortified by indisputable proofs, he gave it to the world. The
immediate effects of his announcement have probably never been
equalled in the history of scientific discovery, unless, perhaps,
in the single instance of the discovery of anaesthesia. In Geneva
and Holland clergymen advocated the practice of vaccination from
their pulpits; in some of the Latin countries religious
processions were formed for receiving vaccination; Jenner's
birthday was celebrated as a feast in Germany; and the first
child vaccinated in Russia was named "Vaccinov" and educated at
public expense. In six years the discovery had penetrated to the
most remote corners of civilization; it had even reached some
savage nations. And in a few years small-pox had fallen from the
position of the most dreaded of all diseases to that of being
practically the only disease for which a sure and easy preventive
was known.

Honors were showered upon Jenner from the Old and the New World,
and even Napoleon, the bitter hater of the English, was among the
others who honored his name.  On one occasion Jenner applied to
the Emperor for the release of certain Englishmen detained in
France.  The petition was about to be rejected when the name of
the petitioner was mentioned. "Ah," said Napoleon, "we can refuse
nothing to that name!"

It is difficult for us of to-day clearly to conceive the
greatness of Jenner's triumph, for we can only vaguely realize
what a ruthless and ever-present scourge smallpox had been to all
previous generations of men since history began.  Despite all
efforts to check it by medication and by direct inoculation, it
swept now and then over the earth as an all-devastating
pestilence, and year by year it claimed one-tenth of all the
beings in Christendom by death as its average quota of victims.
"From small-pox and love but few remain free," ran the old saw. A
pitted face was almost as much a matter of course a hundred years
ago as a smooth one is to-day.

Little wonder, then, that the world gave eager acceptance to
Jenner's discovery.  No urging was needed to induce the majority
to give it trial; passengers on a burning ship do not hold aloof
from the life-boats. Rich and poor, high and low, sought succor
in vaccination and blessed the name of their deliverer. Of all
the great names that were before the world in the closing days of
the century, there was perhaps no other one at once so widely
known and so uniformly reverenced as that of the great English
physician Edward Jenner.  Surely there was no other one that
should be recalled with greater gratitude by posterity.



VIII. NINETEENTH-CENTURY MEDICINE

PHYSICAL DIAGNOSIS

Although Napoleon Bonaparte, First Consul, was not lacking in
self-appreciation, he probably did not realize that in selecting
a physician for his own needs he was markedly influencing the
progress of medical science as a whole.  Yet so strangely are
cause and effect adjusted in human affairs that this simple act
of the First Consul had that very unexpected effect. For the man
chosen was the envoy of a new method in medical practice, and the
fame which came to him through being physician to the First
Consul, and subsequently to the Emperor, enabled him to
promulgate the method in a way otherwise impracticable. Hence the
indirect but telling value to medical science of Napoleon's
selection.

The physician in question was Jean Nicolas de Corvisart.  His
novel method was nothing more startling than the now-familiar
procedure of tapping the chest of a patient to elicit sounds
indicative of diseased tissues within.  Every one has seen this
done commonly enough in our day, but at the beginning of the
century Corvisart, and perhaps some of his pupils, were probably
the only physicians in the world who resorted to this simple and
useful procedure. Hence Napoleon's surprise when, on calling in
Corvisart, after becoming somewhat dissatisfied with his other
physicians Pinel and Portal, his physical condition was
interrogated in this strange manner. With characteristic
shrewdness Bonaparte saw the utility of the method, and the
physician who thus attempted to substitute scientific method for
guess-work in the diagnosis of disease at once found favor in his
eyes and was installed as his regular medical adviser.

For fifteen years before this Corvisart had practised percussion,
as the chest-tapping method is called, without succeeding in
convincing the profession of its value.  The method itself, it
should be added, had not originated with Corvisart, nor did the
French physician for a moment claim it as his own. The true
originator of the practice was the German physician Avenbrugger,
who published a book about it as early as 1761. This book had
even been translated into French, then the language of
international communication everywhere, by Roziere de la
Chassagne, of Montpellier, in 1770; but no one other than
Corvisart appears to have paid any attention to either original
or translation. It was far otherwise, however, when Corvisart
translated Avenbrugger's work anew, with important additions of
his own, in 1808.

"I know very well how little reputation is allotted to translator
and commentators," writes Corvisart, "and I might easily have
elevated myself to the rank of an author if I had elaborated anew
the doctrine of Avenbrugger and published an independent work on
percussion. In this way, however, I should have sacrificed the
name of Avenbrugger to my own vanity, a thing which I am
unwilling to do. It is he, and the beautiful invention which of
right belongs to him, that I desire to recall to life."[1]

By this time a reaction had set in against the metaphysical
methods in medicine that had previously been so alluring; the
scientific spirit of the time was making itself felt in medical
practice; and this, combined with Corvisart's fame, brought the
method of percussion into immediate and well-deserved popularity.
Thus was laid the foundation for the method of so-called physical
diagnosis, which is one of the corner-stones of modern medicine.

The method of physical diagnosis as practised in our day was by
no means completed, however, with the work of Corvisart. 
Percussion alone tells much less than half the story that may be
elicited from the organs of the chest by proper interrogation. 
The remainder of the story can only be learned by applying the
ear itself to the chest, directly or indirectly. Simple as this
seems, no one thought of practising it for some years after
Corvisart had shown the value of percussion.

Then, in 1815, another Paris physician, Rene Theophile Hyacinthe
Laennec, discovered, almost by accident, that the sound of the
heart-beat could be heard surprisingly through a cylinder of
paper held to the ear and against the patient's chest.  Acting on
the hint thus received, Laennec substituted a hollow cylinder of
wood for the paper, and found himself provided with an instrument
through which not merely heart sounds but murmurs of the lungs in
respiration could be heard with almost startling distinctness.

The possibility of associating the varying chest sounds with
diseased conditions of the organs within appealed to the fertile
mind of Laennec as opening new vistas in therapeutics, which he
determined to enter to the fullest extent practicable. His
connection with the hospitals of Paris gave him full opportunity
in this direction, and his labors of the next few years served
not merely to establish the value of the new method as an aid to
diagnosis, but laid the foundation also for the science of morbid
anatomy.  In 1819 Laennec published the results of his labors in
a work called Traite d'Auscultation Mediate,[2] a work which
forms one of the landmarks of scientific medicine. By mediate
auscultation is meant, of course, the interrogation of the chest
with the aid of the little instrument already referred to, an
instrument which its originator thought hardly worth naming until
various barbarous appellations were applied to it by others,
after which Laennec decided to call it the stethoscope, a name
which it has ever since retained.

In subsequent years the form of the stethoscope, as usually
employed, was modified and its value augmented by a binauricular
attachment, and in very recent years a further improvement has
been made through application of the principle of the telephone;
but the essentials of auscultation with the stethoscope were
established in much detail by Laennec, and the honor must always
be his of thus taking one of the longest single steps by which
practical medicine has in our century acquired the right to be
considered a rational science. Laennec's efforts cost him his
life, for he died in 1826 of a lung disease acquired in the
course of his hospital practice; but even before this his fame
was universal, and the value of his method had been recognized
all over the world.  Not long after, in 1828, yet another French
physician, Piorry, perfected the method of percussion by
introducing the custom of tapping, not the chest directly, but
the finger or a small metal or hard-rubber plate held against the
chest-mediate percussion, in short.  This perfected the methods
of physical diagnosis of diseases of the chest in all essentials;
and from that day till this percussion and auscultation have held
an unquestioned place in the regular armamentarium of the
physician.

Coupled with the new method of physical diagnosis in the effort
to substitute knowledge for guess-work came the studies of the
experimental physiologists--in particular, Marshall Hall in
England and Francois Magendie in France; and the joint efforts of
these various workers led presently to the abandonment of those
severe and often irrational depletive methods--blood-letting and
the like--that had previously dominated medical practice. To this
end also the "statistical method," introduced by Louis and his
followers, largely contributed; and by the close of the first
third of our century the idea was gaining ground that the
province of therapeutics is to aid nature in combating disease,
and that this may often be accomplished better by simple means
than by the heroic measures hitherto thought necessary.  In a
word, scientific empiricism was beginning to gain a hearing in
medicine as against the metaphysical preconceptions of the
earlier generations.


PARASITIC DISEASES

I have just adverted to the fact that Napoleon Bonaparte, as
First Consul and as Emperor, was the victim of a malady which
caused him to seek the advice of the most distinguished
physicians of Paris.  It is a little shocking to modern
sensibilities to read that these physicians, except Corvisart,
diagnosed the distinguished patient's malady as "gale
repercutee"--that is to say, in idiomatic English, the itch
"struck in." It is hardly necessary to say that no physician of
today would make so inconsiderate a diagnosis in the case of a
royal patient. If by any chance a distinguished patient were
afflicted with the itch, the sagacious physician would carefully
hide the fact behind circumlocutions and proceed to eradicate the
disease with all despatch.  That the physicians of Napoleon did
otherwise is evidence that at the beginning of the century the
disease in question enjoyed a very different status.  At that
time itch, instead of being a most plebeian malady, was, so to
say, a court disease. It enjoyed a circulation, in high circles
and in low, that modern therapeutics has quite denied it; and the
physicians of the time gave it a fictitious added importance by
ascribing to its influence the existence of almost any obscure
malady that came under their observation. Long after Napoleon's
time gale continued to hold this proud distinction. For example,
the imaginative Dr. Hahnemann did not hesitate to affirm, as a
positive maxim, that three-fourths of all the ills that flesh is
heir to were in reality nothing but various forms of "gale
repercutee."

All of which goes to show how easy it may be for a masked
pretender to impose on credulous humanity, for nothing is more
clearly established in modern knowledge than the fact that "gale
repercutee" was simply a name to hide a profound ignorance; no
such disease exists or ever did exist.  Gale itself is a
sufficiently tangible reality, to be sure, but it is a purely
local disease of the skin, due to a perfectly definite cause, and
the dire internal conditions formerly ascribed to it have really
no causal connection with it whatever. This definite cause, as
every one nowadays knows, is nothing more or less than a
microscopic insect which has found lodgment on the skin, and has
burrowed and made itself at home there. Kill that insect and the
disease is no more; hence it has come to be an axiom with the
modern physician that the itch is one of the three or four
diseases that he positively is able to cure, and that very
speedily.  But it was far otherwise with the physicians of the
first third of our century, because to them the cause of the
disease was an absolute mystery.

It is true that here and there a physician had claimed to find an
insect lodged in the skin of a sufferer from itch, and two or
three times the claim had been made that this was the cause of
the malady, but such views were quite ignored by the general
profession, and in 1833 it was stated in an authoritative medical
treatise that the "cause of gale is absolutely unknown."  But
even at this time, as it curiously happened, there were certain
ignorant laymen who had attained to a bit of medical knowledge
that was withheld from the inner circles of the profession. As
the peasantry of England before Jenner had known of the curative
value of cow-pox over small-pox, so the peasant women of Poland
had learned that the annoying skin disease from which they
suffered was caused by an almost invisible insect, and,
furthermore, had acquired the trick of dislodging the pestiferous
little creature with the point of a needle.  From them a youth of
the country, F. Renucci by name, learned the open secret. He
conveyed it to Paris when he went there to study medicine, and in
1834 demonstrated it to his master Alibert.  This physician, at
first sceptical, soon was convinced, and gave out the discovery
to the medical world with an authority that led to early
acceptance.

Now the importance of all this, in the present connection, is not
at all that it gave the clew to the method of cure of a single
disease. What makes the discovery epochal is the fact that it
dropped a brand-new idea into the medical ranks--an idea
destined, in the long-run, to prove itself a veritable bomb--the
idea, namely, that a minute and quite unsuspected animal parasite
may be the cause of a well-known, widely prevalent, and important
human disease. Of course the full force of this idea could only
be appreciated in the light of later knowledge; but even at the
time of its coming it sufficed to give a great impetus to that
new medical knowledge, based on microscopical studies, which had
but recently been made accessible by the inventions of the
lens-makers. The new knowledge clarified one very turbid medical
pool and pointed the way to the clarification of many others.

Almost at the same time that the Polish medical student was
demonstrating the itch mite in Paris, it chanced, curiously
enough, that another medical student, this time an Englishman,
made an analogous discovery of perhaps even greater importance. 
Indeed, this English discovery in its initial stages slightly
antedated the other, for it was in 1833 that the student in
question, James Paget, interne in St. Bartholomew's Hospital,
London, while dissecting the muscular tissues of a human subject,
found little specks of extraneous matter, which, when taken to
the professor of comparative anatomy, Richard Owen, were
ascertained, with the aid of the microscope, to be the cocoon of
a minute and hitherto unknown insect. Owen named the insect
Trichina spiralis.  After the discovery was published it
transpired that similar specks had been observed by several
earlier investigators, but no one had previously suspected or, at
any rate, demonstrated their nature.  Nor was the full story of
the trichina made out for a long time after Owen's discovery. It
was not till 1847 that the American anatomist Dr. Joseph Leidy
found the cysts of trichina in the tissues of pork; and another
decade or so elapsed after that before German workers, chief
among whom were Leuckart, Virchow, and Zenker, proved that the
parasite gets into the human system through ingestion of infected
pork, and that it causes a definite set of symptoms of disease
which hitherto had been mistaken for rheumatism, typhoid fever,
and other maladies. Then the medical world was agog for a time
over the subject of trichinosis; government inspection of pork
was established in some parts of Germany; American pork was
excluded altogether from France; and the whole subject thus came
prominently to public attention. But important as the trichina
parasite proved on its own account in the end, its greatest
importance, after all, was in the share it played in directing
attention at the time of its discovery in 1833 to the subject of
microscopic parasites in general.

The decade that followed that discovery was a time of great
activity in the study of microscopic organisms and microscopic
tissues, and such men as Ehrenberg and Henle and Bory
Saint-Vincent and Kolliker and Rokitansky and Remak and Dujardin
were widening the bounds of knowledge of this new subject with
details that cannot be more than referred to here. But the
crowning achievement of the period in this direction was the
discovery made by the German, J. L. Schoenlein, in 1839, that a
very common and most distressing disease of the scalp, known as
favus, is really due to the presence and growth on the scalp of a
vegetable organism of microscopic size.  Thus it was made clear
that not merely animal but also vegetable organisms of obscure,
microscopic species have causal relations to the diseases with
which mankind is afflicted. This knowledge of the parasites was
another long step in the direction of scientific medical
knowledge; but the heights to which this knowledge led were not
to be scaled, or even recognized, until another generation of
workers had entered the field.


PAINLESS SURGERY

Meantime, in quite another field of medicine, events were
developing which led presently to a revelation of greater
immediate importance to humanity than any other discovery that
had come in the century, perhaps in any field of science
whatever. This was the discovery of the pain-dispelling power of
the vapor of sulphuric ether inhaled by a patient undergoing a
surgical operation. This discovery came solely out of America,
and it stands curiously isolated, since apparently no minds in
any other country were trending towards it even vaguely.  Davy,
in England, had indeed originated the method of medication by
inhalation, and earned out some most interesting experiments
fifty years earlier, and it was doubtless his experiments with
nitrous oxide gas that gave the clew to one of the American
investigators; but this was the sole contribution of preceding
generations to the subject, and since the beginning of the
century, when Davy turned his attention to other matters, no one
had made the slightest advance along the same line until an
American dentist renewed the investigation.

In view of the sequel, Davy's experiments merit full attention.
Here is his own account of them, as written in 1799:


"Immediately after a journey of one hundred and twenty-six miles,
in which I had no sleep the preceding night, being much
exhausted, I respired seven quarts of nitrous oxide gas for near
three minutes. It produced the usual pleasurable effects and
slight muscular motion. I continued exhilarated for some minutes
afterwards, but in half an hour found myself neither more nor
less exhausted than before the experiment. I had a great
propensity to sleep.

"To ascertain with certainty whether the more extensive action of
nitrous oxide compatible with life was capable of producing
debility, I resolved to breathe the gas for such a time, and in
such quantities, as to produce excitement equal in duration and
superior in intensity to that occasioned by high intoxication
from opium or alcohol.

"To habituate myself to the excitement, and to carry it on
gradually, on December 26th I was enclosed in an air-tight
breathing-box, of the capacity of about nine and one-half cubic
feet, in the presence of Dr. Kinglake.  After I had taken a
situation in which I could by means of a curved thermometer
inserted under the arm, and a stop-watch, ascertain the
alterations in my pulse and animal heat, twenty quarts of nitrous
oxide were thrown into the box.

"For three minutes I experienced no alteration in my sensations,
though immediately after the introduction of the nitrous oxide
the smell and taste of it were very evident.  In four minutes I
began to feel a slight glow in the cheeks and a generally
diffused warmth over the chest, though the temperature of the box
was not quite 50 degrees. . . . In twenty-five minutes the animal
heat was 100 degrees, pulse 124. In thirty minutes twenty quarts
more of gas were introduced.

"My sensations were now pleasant; I had a generally diffused
warmth without the slightest moisture of the skin, a sense of
exhilaration similar to that produced by a small dose of wine,
and a disposition to muscular motion and to merriment.

"In three-quarters of an hour the pulse was 104 and the animal
heat not 99.5 degrees, the temperature of the chamber 64 degrees.
The pleasurable feelings continued to increase, the pulse became
fuller and slower, till in about an hour it was 88, when the
animal heat was 99 degrees. Twenty quarts more of air were
admitted. I had now a great disposition to laugh, luminous points
seemed frequently to pass before my eyes, my hearing was
certainly more acute, and I felt a pleasant lightness and power
of exertion in my muscles. In a short time the symptoms became
stationary; breathing was rather oppressed, and on account of the
great desire for action rest was painful.

"I now came out of the box, having been in precisely an hour and
a quarter. The moment after I began to respire twenty quarts of
unmingled nitrous oxide. A thrilling extending from the chest to
the extremities was almost immediately produced.  I felt a sense
of tangible extension highly pleasurable in every limb; my
visible impressions were dazzling and apparently magnified, I
heard distinctly every sound in the room, and was perfectly aware
of my situation.  By degrees, as the pleasurable sensations
increased, I lost all connection with external things; trains of
vivid visible images rapidly passed through my mind and were
connected with words in such a manner as to produce perceptions
perfectly novel.

"I existed in a world of newly connected and newly modified
ideas. I theorized; I imagined that I made discoveries.  When I
was awakened from this semi-delirious trance by Dr. Kinglake, who
took the bag from my mouth, indignation and pride were the first
feelings produced by the sight of persons about me. My emotions
were enthusiastic and sublime; and for a minute I walked about
the room perfectly regardless of what was said to me. As I
recovered my former state of mind, I felt an inclination to
communicate the discoveries I had made during the experiment. I
endeavored to recall the ideas--they were feeble and indistinct;
one collection of terms, however, presented itself, and, with
most intense belief and prophetic manner, I exclaimed to Dr.
Kinglake, 'Nothing exists but thoughts!--the universe is composed
of impressions, ideas, pleasures, and pains.' "[3]


From this account we see that Davy has anaesthetized himself to a
point where consciousness of surroundings was lost, but not past
the stage of exhilaration.  Had Dr. Kinglake allowed the
inhaling-bag to remain in Davy's mouth for a few moments longer
complete insensibility would have followed. As it was, Davy
appears to have realized that sensibility was dulled, for he adds
this illuminative suggestion: "As nitrous oxide in its extensive
operation appears capable of destroying physical pain, it may
probably be used with advantage during surgical operations in
which no great effusion of blood takes place."[4]

Unfortunately no one took advantage of this suggestion at the
time, and Davy himself became interested in other fields of
science and never returned to his physiological studies, thus
barely missing one of the greatest discoveries in the entire
field of science. In the generation that followed no one seems to
have thought of putting Davy's suggestion to the test, and the
surgeons of Europe had acknowledged with one accord that all hope
of finding a means to render operations painless must be utterly
abandoned--that the surgeon's knife must ever remain a synonym
for slow and indescribable torture. By an odd coincidence it
chanced that Sir Benjamin Brodie, the acknowledged leader of
English surgeons, had publicly expressed this as his deliberate
though regretted opinion at a time when the quest which he
considered futile had already led to the most brilliant success
in America, and while the announcement of the discovery, which
then had no transatlantic cable to convey it, was actually on its
way to the Old World.

The American dentist just referred to, who was, with one
exception to be noted presently, the first man in the world to
conceive that the administration of a definite drug might render
a surgical operation painless and to give the belief application
was Dr. Horace Wells, of Hartford, Connecticut.  The drug with
which he experimented was nitrous oxide--the same that Davy had
used; the operation that he rendered painless was no more
important than the extraction of a tooth--yet it sufficed to mark
a principle; the year of the experiment was 1844.

The experiments of Dr. Wells, however, though important, were not
sufficiently demonstrative to bring the matter prominently to the
attention of the medical world. The drug with which he
experimented proved not always reliable, and he himself seems
ultimately to have given the matter up, or at least to have
relaxed his efforts.  But meantime a friend, to whom he had
communicated his belief and expectations, took the matter up, and
with unremitting zeal carried forward experiments that were
destined to lead to more tangible results. This friend was
another dentist, Dr. W. T. G. Morton, of Boston, then a young man
full of youthful energy and enthusiasm. He seems to have felt
that the drug with which Wells had experimented was not the most
practicable one for the purpose, and so for several months he
experimented with other allied drugs, until finally he hit upon
sulphuric ether, and with this was able to make experiments upon
animals, and then upon patients in the dental chair, that seemed
to him absolutely demonstrative.

Full of eager enthusiasm, and absolutely confident of his
results, he at once went to Dr. J. C. Warren, one of the foremost
surgeons of Boston, and asked permission to test his discovery
decisively on one of the patients at the Boston Hospital during a
severe operation.  The request was granted; the test was made on
October 16, 1846, in the presence of several of the foremost
surgeons of the city and of a body of medical students. The
patient slept quietly while the surgeon's knife was plied, and
awoke to astonished comprehension that the ordeal was over. The
impossible, the miraculous, had been accomplished.[5]

Swiftly as steam could carry it--slowly enough we should think it
to-day--the news was heralded to all the world. It was received
in Europe with incredulity, which vanished before repeated
experiments.  Surgeons were loath to believe that ether, a drug
that had long held a place in the subordinate armamentarium of
the physician, could accomplish such a miracle. But scepticism
vanished before the tests which any surgeon might make, and which
surgeons all over the world did make within the next few weeks. 
Then there came a lingering outcry from a few surgeons, notably
some of the Parisians, that the shock of pain was beneficial to
the patient, hence that anaesthesia--as Dr. Oliver Wendell Holmes
had christened the new method--was a procedure not to be advised. 
Then, too, there came a hue-and-cry from many a pulpit that pain
was God-given, and hence, on moral grounds, to be clung to rather
than renounced. But the outcry of the antediluvians of both
hospital and pulpit quickly received its quietus; for soon it was
clear that the patient who did not suffer the shock of pain
during an operation rallied better than the one who did so
suffer, while all humanity outside the pulpit cried shame to the
spirit that would doom mankind to suffer needless agony.  And so
within a few months after that initial operation at the Boston
Hospital in 1846, ether had made good its conquest of pain
throughout the civilized world. Only by the most active use of
the imagination can we of this present day realize the full
meaning of that victory.

It remains to be added that in the subsequent bickerings over the
discovery--such bickerings as follow every great advance--two
other names came into prominent notice as sharers in the glory of
the new method. Both these were Americans--the one, Dr. Charles
T. Jackson, of Boston; the other, Dr. Crawford W. Long, of
Alabama.  As to Dr. Jackson, it is sufficient to say that he
seems to have had some vague inkling of the peculiar properties
of ether before Morton's discovery. He even suggested the use of
this drug to Morton, not knowing that Morton had already tried
it; but this is the full measure of his association with the
discovery.  Hence it is clear that Jackson's claim to equal share
with Morton in the discovery was unwarranted, not to say absurd.

Dr. Long's association with the matter was far different and
altogether honorable.  By one of those coincidences so common in
the history of discovery, he was experimenting with ether as a
pain-destroyer simultaneously with Morton, though neither so much
as knew of the existence of the other. While a medical student he
had once inhaled ether for the intoxicant effects, as other
medical students were wont to do, and when partially under
influence of the drug he had noticed that a chance blow to his
shins was painless.  This gave him the idea that ether might be
used in surgical operations; and in subsequent years, in the
course of his practice in a small Georgia town, he put the idea
into successful execution. There appears to be no doubt whatever
that he performed successful minor operations under ether some
two or three years before Morton's final demonstration; hence
that the merit of first using the drug, or indeed any drug, in
this way belongs to him. But, unfortunately, Dr. Long did not
quite trust the evidence of his own experiments.  Just at that
time the medical journals were full of accounts of experiments in
which painless operations were said to be performed through
practice of hypnotism, and Dr. Long feared that his own success
might be due to an incidental hypnotic influence rather than to
the drug. Hence he delayed announcing his apparent discovery
until he should have opportunity for further tests--and
opportunities did not come every day to the country practitioner.
And while he waited, Morton anticipated him, and the discovery
was made known to the world without his aid.  It was a true
scientific caution that actuated Dr. Long to this delay, but the
caution cost him the credit, which might otherwise have been his,
of giving to the world one of the greatest blessings--dare we
not, perhaps, say the very greatest?--that science has ever
conferred upon humanity.

A few months after the use of ether became general, the Scotch
surgeon Sir J. Y. Simpson[6] discovered that another drug,
chloroform, could be administered with similar effects; that it
would, indeed, in many cases produce anaesthesia more
advantageously even than ether. From that day till this surgeons
have been more or less divided in opinion as to the relative
merits of the two drugs; but this fact, of course, has no bearing
whatever upon the merit of the first discovery of the method of
anaesthesia.  Even had some other drug subsequently quite
banished ether, the honor of the discovery of the beneficent
method of anaesthesia would have been in no wise invalidated. And
despite all cavillings, it is unequivocally established that the
man who gave that method to the world was William T. G. Morton.


PASTEUR AND THE GERM THEORY OF DISEASE

The discovery of the anaesthetic power of drugs was destined
presently, in addition to its direct beneficences, to aid greatly
in the progress of scientific medicine, by facilitating those
experimental studies of animals from which, before the day of
anaesthesia, many humane physicians were withheld, and which in
recent years have led to discoveries of such inestimable value to
humanity. But for the moment this possibility was quite
overshadowed by the direct benefits of anaesthesia, and the long
strides that were taken in scientific medicine during the first
fifteen years after Morton's discovery were mainly independent of
such aid. These steps were taken, indeed, in a field that at
first glance might seem to have a very slight connection with
medicine. Moreover, the chief worker in the field was not himself
a physician. He was a chemist, and the work in which he was now
engaged was the study of alcoholic fermentation in vinous
liquors. Yet these studies paved the way for the most important
advances that medicine has made in any century towards the plane
of true science; and to this man more than to any other single
individual--it might almost be said more than to all other
individuals--was due this wonderful advance.  It is almost
superfluous to add that the name of this marvellous chemist was
Louis Pasteur.

The studies of fermentation which Pasteur entered upon in 1854
were aimed at the solution of a controversy that had been waging
in the scientific world with varying degrees of activity for a
quarter of a century.  Back in the thirties, in the day of the
early enthusiasm over the perfected microscope, there had arisen
a new interest in the minute forms of life which Leeuwenhoek and
some of the other early workers with the lens had first
described, and which now were shown to be of almost universal
prevalence. These minute organisms had been studied more or less
by a host of observers, but in particular by the Frenchman
Cagniard Latour and the German of cell-theory fame, Theodor
Schwann.  These men, working independently, had reached the
conclusion, about 1837, that the micro-organisms play a vastly
more important role in the economy of nature than any one
previously had supposed. They held, for example, that the minute
specks which largely make up the substance of yeast are living
vegetable organisms, and that the growth of these organisms is
the cause of the important and familiar process of fermentation.
They even came to hold, at least tentatively, the opinion that
the somewhat similar micro-organisms to be found in all
putrefying matter, animal or vegetable, had a causal relation to
the process of putrefaction.

This view, particularly as to the nature of putrefaction, was
expressed even more outspokenly a little later by the French
botanist Turpin.  Views so supported naturally gained a
following; it was equally natural that so radical an innovation
should be antagonized.  In this case it chanced that one of the
most dominating scientific minds of the time, that of Liebig,
took a firm and aggressive stand against the new doctrine. In
1839 he promulgated his famous doctrine of fermentation, in which
he stood out firmly against any "vitalistic" explanation of the
phenomena, alleging that the presence of micro-organisms in
fermenting and putrefying substances was merely incidental, and
in no sense causal.  This opinion of the great German chemist was
in a measure substantiated by experiments of his compatriot
Helmholtz, whose earlier experiments confirmed, but later ones
contradicted, the observations of Schwann, and this combined
authority gave the vitalistic conception a blow from which it had
not rallied at the time when Pasteur entered the field.  Indeed,
it was currently regarded as settled that the early students of
the subject had vastly over-estimated the importance of
micro-organisms.

And so it came as a new revelation to the generality of
scientists of the time, when, in 1857 and the succeeding
half-decade, Pasteur published the results of his researches, in
which the question had been put to a series of altogether new
tests, and brought to unequivocal demonstration.

He proved that the micro-organisms do all that his most
imaginative predecessors had suspected, and more.  Without them,
he proved, there would be no fermentation, no putrefaction--no
decay of any tissues, except by the slow process of oxidation. It
is the microscopic yeast-plant which, by seizing on certain atoms
of the molecule, liberates the remaining atoms in the form of
carbonic-acid and alcohol, thus effecting fermentation; it is
another microscopic plant--a bacterium, as Devaine had christened
it--which in a similar way effects the destruction of organic
molecules, producing the condition which we call putrefaction. 
Pasteur showed, to the amazement of biologists, that there are
certain forms of these bacteria which secure the oxygen which all
organic life requires, not from the air, but by breaking up
unstable molecules in which oxygen is combined; that
putrefaction, in short, has its foundation in the activities of
these so-called anaerobic bacteria.

In a word, Pasteur showed that all the many familiar processes of
the decay of organic tissues are, in effect, forms of
fermentation, and would not take place at all except for the
presence of the living micro-organisms. A piece of meat, for
example, suspended in an atmosphere free from germs, will dry up
gradually, without the slightest sign of putrefaction, regardless
of the temperature or other conditions to which it may have been
subjected. Let us witness one or two series of these experiments
as presented by Pasteur himself in one of his numerous papers
before the Academy of Sciences.


EXPERIMENTS WITH GRAPE SUGAR

"In the course of the discussion which took place before the
Academy upon the subject of the generation of ferments properly
so-called, there was a good deal said about that of wine, the
oldest fermentation known. On this account I decided to disprove
the theory of M. Fremy by a decisive experiment bearing solely
upon the juice of grapes.

"I prepared forty flasks of a capacity of from two hundred and
fifty to three hundred cubic centimetres and filled them half
full with filtered grape-must, perfectly clear, and which, as is
the case of all acidulated liquids that have been boiled for a
few seconds, remains uncontaminated although the curved neck of
the flask containing them remain constantly open during several
months or years.

"In a small quantity of water I washed a part of a bunch of
grapes, the grapes and the stalks together, and the stalks
separately. This washing was easily done by means of a small
badger's-hair brush. The washing-water collected the dust upon
the surface of the grapes and the stalks, and it was easily shown
under the microscope that this water held in suspension a
multitude of minute organisms closely resembling either fungoid
spores, or those of alcoholic Yeast, or those of Mycoderma vini,
etc. This being done, ten of the forty flasks were preserved for
reference; in ten of the remainder, through the straight tube
attached to each, some drops of the washing-water were
introduced; in a third series of ten flasks a few drops of the
same liquid were placed after it had been boiled; and, finally,
in the ten remaining flasks were placed some drops of grape-juice
taken from the inside of a perfect fruit.  In order to carry out
this experiment, the straight tube of each flask was drawn out
into a fine and firm point in the lamp, and then curved. This
fine and closed point was filed round near the end and inserted
into the grape while resting upon some hard substance. When the
point was felt to touch the support of the grape it was by a
slight pressure broken off at the point file mark. Then, if care
had been taken to create a slight vacuum in the flask, a drop of
the juice of the grape got into it, the filed point was
withdrawn, and the aperture immediately closed in the alcohol
lamp.  This decreased pressure of the atmosphere in the flask was
obtained by the following means: After warming the sides of the
flask either in the hands or in the lamp-flame, thus causing a
small quantity of air to be driven out of the end of the curved
neck, this end was closed in the lamp. After the flask was
cooled, there was a tendency to suck in the drop of grape-juice
in the manner just described.

"The drop of grape-juice which enters into the flask by this
suction ordinarily remains in the curved part of the tube, so
that to mix it with the must it was necessary to incline the
flask so as to bring the must into contact with the juice and
then replace the flask in its normal position. The four series of
comparative experiments produced the following results:

"The first ten flasks containing the grape-must boiled in pure
air did not show the production of any organism. The grape-must
could possibly remain in them for an indefinite number of years. 
Those in the second series, containing the water in which the
grapes had been washed separately and together, showed without
exception an alcoholic fermentation which in several cases began
to appear at the end of forty-eight hours when the experiment
took place at ordinary summer temperature. At the same time that
the yeast appeared, in the form of white traces, which little by
little united themselves in the form of a deposit on the sides of
all the flasks, there were seen to form little flakes of
Mycellium, often as a single fungoid growth or in combination,
these fungoid growths being quite independent of the must or of
any alcoholic yeast.  Often, also, the Mycoderma vini appeared
after some days upon the surface of the liquid. The Vibria and
the lactic ferments properly so called did not appear on account
of the nature of the liquid.

"The third series of flasks, the washing-water in which had been
previously boiled, remained unchanged, as in the first series.
Those of the fourth series, in which was the juice of the
interior of the grapes, remained equally free from change,
although I was not always able, on account of the delicacy of the
experiment, to eliminate every chance of error. These experiments
cannot leave the least doubt in the mind as to the following
facts:

Grape-must, after heating, never ferments on contact with the
air, when the air has been deprived of the germs which it
ordinarily holds in a state of suspension.

"The boiled grape-must ferments when there is introduced into it
a very small quantity of water in which the surface of the grapes
or their stalks have been washed.

"The grape-must does not ferment when this washing-water has been
boiled and afterwards cooled.

"The grape-must does not ferment when there is added to it a
small quantity of the juice of the inside of the grape.

"The yeast, therefore, which causes the fermentation of the
grapes in the vintage-tub comes from the outside and not from the
inside of the grapes.  Thus is destroyed the hypothesis of MM. 
Trecol and Fremy, who surmised that the albuminous matter
transformed itself into yeast on account of the vital germs which
were natural to it. With greater reason, therefore, there is no
longer any question of the theory of Liebig of the transformation
of albuminoid matter into ferments on account of the oxidation."


FOREIGN ORGANISMS AND THE WORT OF BEER

"The method which I have just followed," Pasteur continues, "in
order to show that there exists a correlation between the
diseases of beer and certain microscopic organisms leaves no room
for doubt, it seems to me, in regard to the principles I am
expounding.

"Every time that the microscope reveals in the leaven, and
especially in the active yeast, the production of organisms
foreign to the alcoholic yeast properly so called, the flavor of
the beer leaves something to be desired, much or little,
according to the abundance and the character of these little
germs. Moreover, when a finished beer of good quality loses after
a time its agreeable flavor and becomes sour, it can be easily
shown that the alcoholic yeast deposited in the bottles or the
casks, although originally pure, at least in appearance, is found
to be contaminated gradually with these filiform or other
ferments. All this can be deduced from the facts already given,
but some critics may perhaps declare that these foreign ferments
are the consequences of the diseased condition, itself produced
by unknown causes.

"Although this gratuitous hypothesis may be difficult to uphold,
I will endeavor to corroborate the preceding observations by a
clearer method of investigation.  This consists in showing that
the beer never has any unpleasant taste in all cases when the
alcoholic ferment properly so called is not mixed with foreign
ferments; that it is the same in the case of wort, and that wort,
liable to changes as it is, can be preserved unaltered if it is
kept from those microscopic parasites which find in it a suitable
nourishment and a field for growth.

"The employment of this second method has, moreover, the
advantage of proving with certainty the proposition that I
advanced at first--namely, that the germs of these organisms are
derived from the dust of the atmosphere, carried about and
deposited upon all objects, or scattered over the utensils and
the materials used in a brewery-materials naturally charged with
microscopic germs, and which the various operations in the
store-rooms and the malt-house may multiply indefinitely.

"Let us take a glass flask with a long neck of from two hundred
and fifty to three hundred cubic centimetres capacity, and place
in it some wort, with or without hops, and then in the flame of a
lamp draw out the neck of the flask to a fine point, afterwards
heating the liquid until the steam comes out of the end of the
neck. It can then be allowed to cool without any other
precautions; but for additional safety there can be introduced
into the little point a small wad of asbestos at the moment that
the flame is withdrawn from beneath the flask.  Before thus
placing the asbestos it also can be passed through the flame, as
well as after it has been put into the end of the tube. The air
which then first re-enters the flask will thus come into contact
with the heated glass and the heated liquid, so as to destroy the
vitality of any dust germs that may exist in the air.  The air
itself will re-enter very gradually, and slowly enough to enable
any dust to be taken up by the drop of water which the air forces
up the curvature of the tube. Ultimately the tube will be dry,
but the re-entering of the air will be so slow that the particles
of dust will fall upon the sides of the tube.  The experiments
show that with this kind of vessel, allowing free communication
with the air, and the dust not being allowed to enter, the dust
will not enter at all events for a period of ten or twelve years,
which has been the longest period devoted to these trials; and
the liquid, if it were naturally limpid, will not be in the least
polluted neither on its surface nor in its mass, although the
outside of the flask may become thickly coated with dust. This is
a most irrefutable proof of the impossibility of dust getting
inside the flask.

"The wort thus prepared remains uncontaminated indefinitely, in
spite of its susceptibility to change when exposed to the air
under conditions which allow it to gather the dusty particles
which float in the atmosphere. It is the same in the case of
urine, beef-tea, and grape-must, and generally with all those
putrefactable and fermentable liquids which have the property
when heated to boiling-point of destroying the vitality of dust
germs."[7]


There was nothing in these studies bearing directly upon the
question of animal diseases, yet before they were finished they
had stimulated progress in more than one field of pathology. At
the very outset they sufficed to start afresh the inquiry as to
the role played by micro-organisms in disease. In particular they
led the French physician Devaine to return to some interrupted
studies which he had made ten years before in reference to the
animal disease called anthrax, or splenic fever, a disease that
cost the farmers of Europe millions of francs annually through
loss of sheep and cattle. In 1850 Devaine had seen multitudes of
bacteria in the blood of animals who had died of anthrax, but he
did not at that time think of them as having a causal relation to
the disease. Now, however, in 1863, stimulated by Pasteur's new
revelations regarding the power of bacteria, he returned to the
subject, and soon became convinced, through experiments by means
of inoculation, that the microscopic organisms he had discovered
were the veritable and the sole cause of the infectious disease
anthrax.

The publication of this belief in 1863 aroused a furor of
controversy. That a microscopic vegetable could cause a virulent
systemic disease was an idea altogether too startling to be
accepted in a day, and the generality of biologists and
physicians demanded more convincing proofs than Devaine as yet
was able to offer.

Naturally a host of other investigators all over the world
entered the field. Foremost among these was the German Dr. Robert
Koch, who soon corroborated all that Devaine had observed, and
carried the experiments further in the direction of the
cultivation of successive generations of the bacteria in
artificial media, inoculations being made from such pure cultures
of the eighth generation, with the astonishing result that
animals thus inoculated succumbed to the disease.

Such experiments seem demonstrative, yet the world was
unconvinced, and in 1876, while the controversy was still at its
height, Pasteur was prevailed upon to take the matter in hand.
The great chemist was becoming more and more exclusively a
biologist as the years passed, and in recent years his famous
studies of the silk-worm diseases, which he proved due to
bacterial infection, and of the question of spontaneous
generation, had given him unequalled resources in microscopical
technique. And so when, with the aid of his laboratory associates
Duclaux and Chamberland and Roux, he took up the mooted anthrax
question the scientific world awaited the issue with bated
breath. And when, in 1877, Pasteur was ready to report on his
studies of anthrax, he came forward with such a wealth of
demonstrative experiments--experiments the rigid accuracy of
which no one would for a moment think of questioning--going to
prove the bacterial origin of anthrax, that scepticism was at
last quieted for all time to come.

Henceforth no one could doubt that the contagious disease anthrax
is due exclusively to the introduction into an animal's system of
a specific germ--a microscopic plant--which develops there. And
no logical mind could have a reasonable doubt that what is proved
true of one infectious disease would some day be proved true also
of other, perhaps of all, forms of infectious maladies.

Hitherto the cause of contagion, by which certain maladies spread
from individual to individual, had been a total mystery, quite
unillumined by the vague terms "miasm," "humor," "virus," and the
like cloaks of ignorance.  Here and there a prophet of science,
as Schwann and Henle, had guessed the secret; but guessing, in
science, is far enough from knowing. Now, for the first time, the
world KNEW, and medicine had taken another gigantic stride
towards the heights of exact science.


LISTER AND ANTISEPTIC SURGERY

Meantime, in a different though allied field of medicine there
had been a complementary growth that led to immediate results of
even more practical importance.  I mean the theory and practice
of antisepsis in surgery.  This advance, like the other, came as
a direct outgrowth of Pasteur's fermentation studies of alcoholic
beverages, though not at the hands of Pasteur himself. Struck by
the boundless implications of Pasteur's revelations regarding the
bacteria, Dr. Joseph Lister (the present Lord Lister), then of
Glasgow, set about as early as 1860 to make a wonderful
application of these ideas. If putrefaction is always due to
bacterial development, he argued, this must apply as well to
living as to dead tissues; hence the putrefactive changes which
occur in wounds and after operations on the human subject, from
which blood-poisoning so often follows, might be absolutely
prevented if the injured surfaces could be kept free from access
of the germs of decay.

In the hope of accomplishing this result, Lister began
experimenting with drugs that might kill the bacteria without
injury to the patient, and with means to prevent further access
of germs once a wound was freed from them. How well he succeeded
all the world knows; how bitterly he was antagonized for about a
score of years, most of the world has already forgotten. As early
as 1867 Lister was able to publish results pointing towards
success in his great project; yet so incredulous were surgeons in
general that even some years later the leading surgeons on the
Continent had not so much as heard of his efforts.  In 1870 the
soldiers of Paris died, as of old, of hospital gangrene; and
when, in 1871, the French surgeon Alphonse Guerin, stimulated by
Pasteur's studies, conceived the idea of dressing wounds with
cotton in the hope of keeping germs from entering them, he was
quite unaware that a British contemporary had preceded him by a
full decade in this effort at prevention and had made long
strides towards complete success. Lister's priority, however, and
the superiority of his method, were freely admitted by the French
Academy of Sciences, which in 1881 officially crowned his
achievement, as the Royal Society of London had done the year
before.

By this time, to be sure, as everybody knows, Lister's new
methods had made their way everywhere, revolutionizing the
practice of surgery and practically banishing from the earth
maladies that hitherto had been the terror of the surgeon and the
opprobrium of his art. And these bedside studies, conducted in
the end by thousands of men who had no knowledge of microscopy,
had a large share in establishing the general belief in the
causal relation that micro-organisms bear to disease, which by
about the year 1880 had taken possession of the medical world.
But they did more; they brought into equal prominence the idea
that, the cause of a diseased condition being known, it maybe
possible as never before to grapple with and eradicate that
condition.


PREVENTIVE INOCULATION

The controversy over spontaneous generation, which, thanks to
Pasteur and Tyndall, had just been brought to a termination, made
it clear that no bacterium need be feared where an antecedent
bacterium had not found lodgment; Listerism in surgery had now
shown how much might be accomplished towards preventing the
access of germs to abraded surfaces of the body and destroying
those that already had found lodgment there. As yet, however,
there was no inkling of a way in which a corresponding onslaught
might be made upon those other germs which find their way into
the animal organism by way of the mouth and the nostrils, and
which, as was now clear, are the cause of those contagious
diseases which, first and last, claim so large a proportion of
mankind for their victims. How such means might be found now
became the anxious thought of every imaginative physician, of
every working microbiologist.

As it happened, the world was not kept long in suspense. Almost
before the proposition had taken shape in the minds of the other
leaders, Pasteur had found a solution. Guided by the empirical
success of Jenner, he, like many others, had long practised
inoculation experiments, and on February 9, 1880, he announced to
the French Academy of Sciences that he had found a method of so
reducing the virulence of a disease germ that when introduced
into the system of a susceptible animal it produced only a mild
form of the disease, which, however, sufficed to protect against
the usual virulent form exactly as vaccinia protects against
small-pox. The particular disease experimented with was that
infectious malady of poultry known familiarly as "chicken
cholera."  In October of the same year Pasteur announced the
method by which this "attenuation of the virus," as he termed it,
had been brought about--by cultivation of the disease germs in
artificial media, exposed to the air, and he did not hesitate to
assert his belief that the method would prove "susceptible of
generalization"--that is to say, of application to other diseases
than the particular one in question.

Within a few months he made good this prophecy, for in February,
1881, he announced to the Academy that with the aid, as before,
of his associates MM.  Chamberland and Roux, he had produced an
attenuated virus of the anthrax microbe by the use of which, as
he affirmed with great confidence, he could protect sheep, and
presumably cattle, against that fatal malady.  "In some recent
publications," said Pasteur, "I announced the first case of the
attenuation of a virus by experimental methods only. Formed of a
special microbe of an extreme minuteness, this virus may be
multiplied by artificial culture outside the animal body. These
cultures, left alone without any possible external contamination,
undergo, in the course of time, modifications of their virulency
to a greater or less extent.  The oxygen of the atmosphere is
said to be the chief cause of these attenuations--that is, this
lessening of the facilities of multiplication of the microbe; for
it is evident that the difference of virulence is in some way
associated with differences of development in the parasitic
economy.

"There is no need to insist upon the interesting character of
these results and the deductions to be made therefrom. To seek to
lessen the virulence by rational means would be to establish,
upon an experimental basis, the hope of preparing from an active
virus, easily cultivated either in the human or animal body, a
vaccine-virus of restrained development capable of preventing the
fatal effects of the former. Therefore, we have applied all our
energies to investigate the possible generalizing action of
atmospheric oxygen in the attenuation of virus.

"The anthrax virus, being one that has been most carefully
studied, seemed to be the first that should attract our
attention. Every time, however, we encountered a difficulty.
Between the microbe of chicken cholera and the microbe of anthrax
there exists an essential difference which does not allow the new
experiment to be verified by the old. The microbes of chicken
cholera do not, in effect, seem to resolve themselves, in their
culture, into veritable germs. The latter are merely cells, or
articulations always ready to multiply by division, except when
the particular conditions in which they become true germs are
known.

"The yeast of beer is a striking example of these cellular
productions, being able to multiply themselves indefinitely
without the apparition of their original spores.  There exist
many mucedines (Mucedinae?) of tubular mushrooms, which in
certain conditions of culture produce a chain of more or less
spherical cells called Conidae.  The latter, detached from their
branches, are able to reproduce themselves in the form of cells,
without the appearance, at least with a change in the conditions
of culture, of the spores of their respective mucedines. These
vegetable organisms can be compared to plants which are
cultivated by slipping, and to produce which it is not necessary
to have the fruits or the seeds of the mother plant.

The anthrax bacterium, in its artificial cultivation, behaves
very differently.  Its mycelian filaments, if one may so describe
them, have been produced scarcely for twenty-four or forty-eight
hours when they are seen to transform themselves, those
especially which are in free contact with the air, into very
refringent corpuscles, capable of gradually isolating themselves
into true germs of slight organization.  Moreover, observation
shows that these germs, formed so quickly in the culture, do not
undergo, after exposure for a time to atmospheric air, any change
either in their vitality or their virulence. I was able to
present to the Academy a tube containing some spores of anthrax
bacteria produced four years ago, on March 21, 1887. Each year
the germination of these little corpuscles has been tried, and
each year the germination has been accomplished with the same
facility and the same rapidity as at first. Each year also the
virulence of the new cultures has been tested, and they have not
shown any visible falling off.  Therefore, how can we experiment
with the action of the air upon the anthrax virus with any
expectation of making it less virulent?

"The crucial difficulty lies perhaps entirely in this rapid
reproduction of the bacteria germs which we have just related. In
its form of a filament, and in its multiplication by division, is
not this organism at all points comparable with the microbe of
the chicken cholera?

"That a germ, properly so called, that a seed, does not suffer
any modification on account of the air is easily conceived; but
it is conceivable not less easily that if there should be any
change it would occur by preference in the case of a mycelian
fragment. It is thus that a slip which may have been abandoned in
the soil in contact with the air does not take long to lose all
vitality, while under similar conditions a seed is preserved in
readiness to reproduce the plant.  If these views have any
foundation, we are led to think that in order to prove the action
of the air upon the anthrax bacteria it will be indispensable to
submit to this action the mycelian development of the minute
organism under conditions where there cannot be the least
admixture of corpuscular germs. Hence the problem of submitting
the bacteria to the action of oxygen comes back to the question
of presenting entirely the formation of spores. The question
being put in this way, we are beginning to recognize that it is
capable of being solved.

"We can, in fact, prevent the appearance of spores in the
artificial cultures of the anthrax parasite by various artifices.
At the lowest temperature at which this parasite can be
cultivated--that is to say, about +16 degrees Centigrade--the
bacterium does not produce germs--at any rate, for a very long
time. The shapes of the minute microbe at this lowest limit of
its development are irregular, in the form of balls and pears--in
a word, they are monstrosities--but they are without spores. In
the last regard also it is the same at the highest temperatures
at which the parasite can be cultivated, temperatures which vary
slightly according to the means employed. In neutral chicken
bouillon the bacteria cannot be cultivated above 45 degrees.
Culture, however, is easy and abundant at 42 to 43 degrees, but
equally without any formation of spores.  Consequently a culture
of mycelian bacteria can be kept entirely free from germs while
in contact with the open air at a temperature of from 42 to 43
degrees Centigrade.  Now appear the three remarkable results.
After about one month of waiting the culture dies--that is to
say, if put into a fresh bouillon it becomes absolutely sterile.

"So much for the life and nutrition of this organism. In respect
to its virulence, it is an extraordinary fact that it disappears
entirely after eight days' culture at 42 to 43 degrees
Centigrade, or, at any rate, the cultures are innocuous for the
guinea-pig, the rabbit, and the sheep, the three kinds of animals
most apt to contract anthrax. We are thus able to obtain, not
only the attenuation of the virulence, but also its complete
suppression by a simple method of cultivation. Moreover, we see
also the possibility of preserving and cultivating the terrible
microbe in an inoffensive state. What is it that happens in these
eight days at 43 degrees that suffices to take away the virulence
of the bacteria? Let us remember that the microbe of chicken
cholera dies in contact with the air, in a period somewhat
protracted, it is true, but after successive attenuations.  Are
we justified in thinking that it ought to be the same in regard
to the microbe of anthrax?  This hypothesis is confirmed by
experiment. Before the disappearance of its virulence the anthrax
microbe passes through various degrees of attenuation, and,
moreover, as is also the case with the microbe of chicken
cholera, each of these attenuated states of virulence can be
obtained by cultivation. Moreover, since, according to one of our
recent Communications, anthrax is not recurrent, each of our
attenuated anthrax microbes is, for the better-developed microbe,
a vaccine--that is to say, a virus producing a less-malignant
malady. What, therefore, is easier than to find in these a virus
that will infect with anthrax sheep, cows, and horses, without
killing them, and ultimately capable of warding off the mortal
malady? We have practised this experiment with great success upon
sheep, and when the season comes for the assembling of the flocks
at Beauce we shall try the experiment on a larger scale.

"Already M. Toussaint has announced that sheep can be saved by
preventive inoculations; but when this able observer shall have
published his results; on the subject of which we have made such
exhaustive studies, as yet unpublished, we shall be able to see
the whole difference which exists between the two methods--the
uncertainty of the one and the certainty of the other. That which
we announce has, moreover, the very great advantage of resting
upon the existence of a poison vaccine cultivable at will, and
which can be increased indefinitely in the space of a few hours
without having recourse to infected blood."[8]


This announcement was immediately challenged in a way that
brought it to the attention of the entire world. The president of
an agricultural society, realizing the enormous importance of the
subject, proposed to Pasteur that his alleged discovery should be
submitted to a decisive public test. He proposed to furnish a
drove of fifty sheep half of which were to be inoculated with the
attenuated virus of Pasteur.  Subsequently all the sheep were to
be inoculated with virulent virus, all being kept together in one
pen under precisely the same conditions. The "protected" sheep
were to remain healthy; the unprotected ones to die of anthrax;
so read the terms of the proposition. Pasteur accepted the
challenge; he even permitted a change in the programme by which
two goats were substituted for two of the sheep, and ten cattle
added, stipulating, however, that since his experiments had not
yet been extended to cattle these should not be regarded as
falling rigidly within the terms of the test.

It was a test to try the soul of any man, for all the world
looked on askance, prepared to deride the maker of so
preposterous a claim as soon as his claim should be proved
baseless. Not even the fame of Pasteur could make the public at
large, lay or scientific, believe in the possibility of what he
proposed to accomplish.  There was time for all the world to be
informed of the procedure, for the first "preventive"
inoculation--or vaccination, as Pasteur termed it--was made on
May 5th, the second on May 17th, and another interval of two
weeks must elapse before the final inoculations with the
unattenuated virus. Twenty-four sheep, one goat, and five cattle
were submitted to the preliminary vaccinations.  Then, on May 31
st, all sixty of the animals were inoculated, a protected and
unprotected one alternately, with an extremely virulent culture
of anthrax microbes that had been in Pasteur's laboratory since
1877. This accomplished, the animals were left together in one
enclosure to await the issue.

Two days later, June 2d, at the appointed hour of rendezvous, a
vast crowd, composed of veterinary surgeons, newspaper
correspondents, and farmers from far and near, gathered to
witness the closing scenes of this scientific tourney. What they
saw was one of the most dramatic scenes in the history of
peaceful science--a scene which, as Pasteur declared afterwards,
"amazed the assembly."  Scattered about the enclosure, dead,
dying, or manifestly sick unto death, lay the unprotected
animals, one and all, while each and every "protected" animal
stalked unconcernedly about with every appearance of perfect
health. Twenty of the sheep and the one goat were already dead;
two other sheep expired under the eyes of the spectators; the
remaining victims lingered but a few hours longer. Thus in a
manner theatrical enough, not to say tragic, was proclaimed the
unequivocal victory of science. Naturally enough, the unbelievers
struck their colors and surrendered without terms; the principle
of protective vaccination, with a virus experimentally prepared
in the laboratory, was established beyond the reach of
controversy.

That memorable scientific battle marked the beginning of a new
era in medicine.  It was a foregone conclusion that the principle
thus established would be still further generalized; that it
would be applied to human maladies; that in all probability it
would grapple successfully, sooner or later, with many infectious
diseases. That expectation has advanced rapidly towards
realization. Pasteur himself made the application to the human
subject in the disease hydrophobia in 1885, since which time that
hitherto most fatal of maladies has largely lost its terrors. 
Thousands of persons bitten by mad dogs have been snatched from
the fatal consequences of that mishap by this method at the
Pasteur Institute in Paris, and at the similar institutes, built
on the model of this parent one, that have been established all
over the world in regions as widely separated as New York and
Nha-Trang.


SERUM-THERAPY

In the production of the rabies vaccine Pasteur and his
associates developed a method of attenuation of a virus quite
different from that which had been employed in the case of the
vaccines of chicken cholera and of anthrax. The rabies virus was
inoculated into the system of guinea-pigs or rabbits and, in
effect, cultivated in the systems of these animals. The spinal
cord of these infected animals was found to be rich in the virus,
which rapidly became attenuated when the cord was dried in the
air.  The preventive virus, of varying strengths, was made by
maceration of these cords at varying stages of desiccation. This
cultivation of a virus within the animal organism suggested, no
doubt, by the familiar Jennerian method of securing small-pox
vaccine, was at the same time a step in the direction of a new
therapeutic procedure which was destined presently to become of
all-absorbing importance--the method, namely, of so-called
serum-therapy, or the treatment of a disease with the blood serum
of an animal that has been subjected to protective inoculation
against that disease.

The possibility of such a method was suggested by the familiar
observation, made by Pasteur and numerous other workers, that
animals of different species differ widely in their
susceptibility to various maladies, and that the virus of a given
disease may become more and more virulent when passed through the
systems of successive individuals of one species, and,
contrariwise, less and less virulent when passed through the
systems of successive individuals of another species. These facts
suggested the theory that the blood of resistant animals might
contain something directly antagonistic to the virus, and the
hope that this something might be transferred with curative
effect to the blood of an infected susceptible animal. Numerous
experimenters all over the world made investigations along the
line of this alluring possibility, the leaders perhaps being Drs. 
Behring and Kitasato, closely followed by Dr. Roux and his
associates of the Pasteur Institute of Paris.  Definite results
were announced by Behring in 1892 regarding two important
diseases--tetanus and diphtheria--but the method did not come
into general notice until 1894, when Dr. Roux read an
epoch-making paper on the subject at the Congress of Hygiene at
Buda-Pesth.

In this paper Dr. Roux, after adverting to the labors of Behring,
Ehrlich, Boer, Kossel, and Wasserman, described in detail the
methods that had been developed at the Pasteur Institute for the
development of the curative serum, to which Behring had given the
since-familiar name antitoxine. The method consists, first, of
the cultivation, for some months, of the diphtheria bacillus
(called the Klebs-Loeffler bacillus, in honor of its discoverers)
in an artificial bouillon, for the development of a powerful
toxine capable of giving the disease in a virulent form.

This toxine, after certain details of mechanical treatment, is
injected in small but increasing doses into the system of an
animal, care being taken to graduate the amount so that the
animal does not succumb to the disease. After a certain course of
this treatment it is found that a portion of blood serum of the
animal so treated will act in a curative way if injected into the
blood of another animal, or a human patient, suffering with
diphtheria. In other words, according to theory, an antitoxine
has been developed in the system of the animal subjected to the
progressive inoculations of the diphtheria toxine.  In Dr. Roux's
experience the animal best suited for the purpose is the horse,
though almost any of the domesticated animals will serve the
purpose.

But Dr. Roux's paper did not stop with the description of
laboratory methods. It told also of the practical application of
the serum to the treatment of numerous cases of diphtheria in the
hospitals of Paris--applications that had met with a gratifying
measure of success.  He made it clear that a means had been found
of coping successfully with what had been one of the most
virulent and intractable of the diseases of childhood. Hence it
was not strange that his paper made a sensation in all circles,
medical and lay alike.

Physicians from all over the world flocked to Paris to learn the
details of the open secret, and within a few months the new
serum-therapy had an acknowledged standing with the medical
profession everywhere. What it had accomplished was regarded as
but an earnest of what the new method might accomplish presently
when applied to the other infectious diseases.

Efforts at such applications were immediately begun in numberless
directions--had, indeed, been under way in many a laboratory for
some years before. It is too early yet to speak of the results in
detail. But enough has been done to show that this method also is
susceptible of the widest generalization.  It is not easy at the
present stage to sift that which is tentative from that which
will be permanent; but so great an authority as Behring does not
hesitate to affirm that today we possess, in addition to the
diphtheria antitoxine, equally specific antitoxines of tetanus,
cholera, typhus fever, pneumonia, and tuberculosis--a set of
diseases which in the aggregate account for a startling
proportion of the general death-rate. Then it is known that Dr.
Yersin, with the collaboration of his former colleagues of the
Pasteur Institute, has developed, and has used with success, an
antitoxine from the microbe of the plague which recently ravaged
China.

Dr. Calmette, another graduate of the Pasteur Institute, has
extended the range of the serum-therapy to include the prevention
and treatment of poisoning by venoms, and has developed an
antitoxine that has already given immunity from the lethal
effects of snake bites to thousands of persons in India and
Australia.

Just how much of present promise is tentative, just what are the
limits of the methods--these are questions for the future to
decide. But, in any event, there seems little question that the
serum treatment will stand as the culminating achievement in
therapeutics of our century. It is the logical outgrowth of those
experimental studies with the microscope begun by our
predecessors of the thirties, and it represents the present
culmination of the rigidly experimental method which has brought
medicine from a level of fanciful empiricism to the plane of a
rational experimental science.



IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY

BRAIN AND MIND

A little over a hundred years ago a reform movement was afoot in
the world in the interests of the insane. As was fitting, the
movement showed itself first in America, where these unfortunates
were humanely cared for at a time when their treatment elsewhere
was worse than brutal; but England and France quickly fell into
line.  The leader on this side of the water was the famous
Philadelphian, Dr. Benjamin Rush, "the Sydenham of America"; in
England, Dr. William Tuke inaugurated the movement; and in
France, Dr. Philippe Pinel, single-handed, led the way. Moved by
a common spirit, though acting quite independently, these men
raised a revolt against the traditional custom which, spurning
the insane as demon-haunted outcasts, had condemned these
unfortunates to dungeons, chains, and the lash. Hitherto few
people had thought it other than the natural course of events
that the "maniac" should be thrust into a dungeon, and perhaps
chained to the wall with the aid of an iron band riveted
permanently about his neck or waist. Many an unfortunate, thus
manacled, was held to the narrow limits of his chain for years
together in a cell to which full daylight never penetrated;
sometimes--iron being expensive--the chain was so short that the
wretched victim could not rise to the upright posture or even
shift his position upon his squalid pallet of straw.

In America, indeed, there being no Middle Age precedents to
crystallize into established customs, the treatment accorded the
insane had seldom or never sunk to this level. Partly for this
reason, perhaps, the work of Dr. Rush at the Philadelphia
Hospital, in 1784, by means of which the insane came to be
humanely treated, even to the extent of banishing the lash, has
been but little noted, while the work of the European leaders,
though belonging to later decades, has been made famous. And
perhaps this is not as unjust as it seems, for the step which
Rush took, from relatively bad to good, was a far easier one to
take than the leap from atrocities to good treatment which the
European reformers were obliged to compass. In Paris, for
example, Pinel was obliged to ask permission of the authorities
even to make the attempt at liberating the insane from their
chains, and, notwithstanding his recognized position as a leader
of science, he gained but grudging assent, and was regarded as
being himself little better than a lunatic for making so
manifestly unwise and hopeless an attempt. Once the attempt had
been made, however, and carried to a successful issue, the
amelioration wrought in the condition of the insane was so patent
that the fame of Pinel's work at the Bicetre and the Salpetriere
went abroad apace. It required, indeed, many years to complete it
in Paris, and a lifetime of effort on the part of Pinel's pupil
Esquirol and others to extend the reform to the provinces; but
the epochal turning-point had been reached with Pinel's labors of
the closing years of the eighteenth century.

The significance of this wise and humane reform, in the present
connection, is the fact that these studies of the insane gave
emphasis to the novel idea, which by-and-by became accepted as
beyond question, that "demoniacal possession" is in reality no
more than the outward expression of a diseased condition of the
brain. This realization made it clear, as never before, how
intimately the mind and the body are linked one to the other. 
And so it chanced that, in striking the shackles from the insane,
Pinel and his confreres struck a blow also, unwittingly, at
time-honored philosophical traditions. The liberation of the
insane from their dungeons was an augury of the liberation of
psychology from the musty recesses of metaphysics. Hitherto
psychology, in so far as it existed at all, was but the
subjective study of individual minds; in future it must become
objective as well, taking into account also the relations which
the mind bears to the body, and in particular to the brain and
nervous system.

The necessity for this collocation was advocated quite as
earnestly, and even more directly, by another worker of this
period, whose studies were allied to those of alienists, and who,
even more actively than they, focalized his attention upon the
brain and its functions. This earliest of specialists in brain
studies was a German by birth but Parisian by adoption, Dr. Franz
Joseph Gall, originator of the since-notorious system of
phrenology.  The merited disrepute into which this system has
fallen through the exposition of peripatetic charlatans should
not make us forget that Dr. Gall himself was apparently a highly
educated physician, a careful student of the brain and mind
according to the best light of his time, and, withal, an earnest
and honest believer in the validity of the system he had
originated. The system itself, taken as a whole, was hopelessly
faulty, yet it was not without its latent germ of truth, as later
studies were to show. How firmly its author himself believed in
it is evidenced by the paper which he contributed to the French
Academy of Sciences in 1808. The paper itself was referred to a
committee of which Pinel and Cuvier were members.  The verdict of
this committee was adverse, and justly so; yet the system
condemned had at least one merit which its detractors failed to
realize.  It popularized the conception that the brain is the
organ of mind.  Moreover, by its insistence it rallied about it a
band of scientific supporters, chief of whom was Dr. Kaspar
Spurzlieim, a man of no mean abilities, who became the
propagandist of phrenology in England and in America.  Of course
such advocacy and popularity stimulated opposition as well, and
out of the disputations thus arising there grew presently a
general interest in the brain as the organ of mind, quite aside
from any preconceptions whatever as to the doctrines of Gall and
Spurzheim.

Prominent among the unprejudiced class of workers who now
appeared was the brilliant young Frenchman Louis Antoine
Desmoulins, who studied first under the tutorage of the famous
Magendie, and published jointly with him a classical work on the
nervous system of vertebrates in 1825. Desmoulins made at least
one discovery of epochal importance. He observed that the brains
of persons dying in old age were lighter than the average and
gave visible evidence of atrophy, and he reasoned that such decay
is a normal accompaniment of senility. No one nowadays would
question the accuracy of this observation, but the scientific
world was not quite ready for it in 1825; for when Desmoulins
announced his discovery to the French Academy, that august and
somewhat patriarchal body was moved to quite unscientific wrath,
and forbade the young iconoclast the privilege of further
hearings. From which it is evident that the partially liberated
spirit of the new psychology had by no means freed itself
altogether, at the close of the first quarter of the nineteenth
century, from the metaphysical cobwebs of its long incarceration.


FUNCTIONS OF THE NERVES

While studies of the brain were thus being inaugurated, the
nervous system, which is the channel of communication between the
brain and the outside world, was being interrogated with even
more tangible results.  The inaugural discovery was made in 1811
by Dr. (afterwards Sir Charles) Bell,[1] the famous English
surgeon and experimental physiologist. It consisted of the
observation that the anterior roots of the spinal nerves are
given over to the function of conveying motor impulses from the
brain outward, whereas the posterior roots convey solely sensory
impulses to the brain from without. Hitherto it had been supposed
that all nerves have a similar function, and the peculiar
distribution of the spinal nerves had been an unsolved puzzle.

Bell's discovery was epochal; but its full significance was not
appreciated for a decade, nor, indeed, was its validity at first
admitted.  In Paris, in particular, then the court of final
appeal in all matters scientific, the alleged discovery was
looked at askance, or quite ignored.  But in 1823 the subject was
taken up by the recognized leader of French physiology--Francois
Magendie--in the course of his comprehensive experimental studies
of the nervous system, and Bell's conclusions were subjected to
the most rigid experimental tests and found altogether valid.
Bell himself, meanwhile, had turned his attention to the cranial
nerves, and had proved that these also are divisible into two
sets--sensory and motor.  Sometimes, indeed, the two sets of
filaments are combined into one nerve cord, but if traced to
their origin these are found to arise from different brain
centres. Thus it was clear that a hitherto unrecognized duality
of function pertains to the entire extra-cranial nervous system.
Any impulse sent from the periphery to the brain must be conveyed
along a perfectly definite channel; the response from the brain,
sent out to the peripheral muscles, must traverse an equally
definite and altogether different course.  If either channel is
interrupted--as by the section of its particular nerve tract--the
corresponding message is denied transmission as effectually as an
electric current is stopped by the section of the transmitting
wire.

Experimenters everywhere soon confirmed the observations of Bell
and Magendie, and, as always happens after a great discovery, a
fresh impulse was given to investigations in allied fields. 
Nevertheless, a full decade elapsed before another discovery of
comparable importance was made. Then Marshall Hall, the most
famous of English physicians of his day, made his classical
observations on the phenomena that henceforth were to be known as
reflex action.  In 1832, while experimenting one day with a
decapitated newt, he observed that the headless creature's limbs
would contract in direct response to certain stimuli.  Such a
response could no longer be secured if the spinal nerves
supplying a part were severed. Hence it was clear that responsive
centres exist in the spinal cord capable of receiving a sensory
message and of transmitting a motor impulse in reply--a function
hitherto supposed to be reserved for the brain. Further studies
went to show that such phenomena of reflex action on the part of
centres lying outside the range of consciousness, both in the
spinal cord and in the brain itself, are extremely common; that,
in short, they enter constantly into the activities of every
living organism and have a most important share in the sum total
of vital movements. Hence, Hall's discovery must always stand as
one of the great mile-stones of the advance of neurological
science.

Hall gave an admirably clear and interesting account of his
experiments and conclusions in a paper before the Royal Society,
"On the Reflex Functions of the Medulla Oblongata and the Medulla
Spinalis," from which, as published in the Transactions of the
society for 1833, we may quote at some length:

"In the entire animal, sensation and voluntary motion, functions
of the cerebrum, combine with the functions of the medulla
oblongata and medulla spinalis, and may therefore render it
difficult or impossible to determine those which are peculiar to
each; if, in an animal deprived of the brain, the spinal marrow
or the nerves supplying the muscles be stimulated, those muscles,
whether voluntary or respiratory, are equally thrown into
contraction, and, it may be added, equally in the complete and in
the mutilated animal; and, in the case of the nerves, equally in
limbs connected with and detached from the spinal marrow.

"The operation of all these various causes may be designated
centric, as taking place AT, or at least in a direction FROM,
central parts of the nervous system.  But there is another
function the phenomena of which are of a totally different order
and obey totally different laws, being excited by causes in a
situation which is EXCENTRIC in the nervous system--that is,
distant from the nervous centres. This mode of action has not, I
think, been hitherto distinctly understood by physiologists.

"Many of the phenomena of this principle of action, as they occur
in the limbs, have certainly been observed.  But, in the first
place, this function is by no means confined to the limbs; for,
while it imparts to each muscle its appropriate tone, and to each
system of muscles its appropriate equilibrium or balance, it
performs the still more important office of presiding over the
orifices and terminations of each of the internal canals in the
animal economy, giving them their due form and action; and, in
the second place, in the instances in which the phenomena of this
function have been noticed, they have been confounded, as I have
stated, with those of sensation and volition; or, if they have
been distinguished from these, they have been too indefinitely
denominated instinctive, or automatic. I have been compelled,
therefore, to adopt some new designation for them, and I shall
now give the reasons for my choice of that which is given in the
title of this paper--'Reflex Functions.'

"This property is characterized by being EXCITED in its action
and REFLEX in its course:  in every instance in which it is
exerted an impression made upon the extremities of certain nerves
is conveyed to the medulla oblongata or the medulla spinalis, and
is reflected along the nerves to parts adjacent to, or remote
from, that which has received the impression.

"It is by this reflex character that the function to which I have
alluded is to be distinguished from every other. There are, in
the animal economy, four modes of muscular action, of muscular
contraction.  The first is that designated VOLUNTARY: volition,
originated in the cerebrum and spontaneous in its acts, extends
its influence along the spinal marrow and the motor nerves in a
DIRECT LINE to the voluntary muscles. The SECOND is that of
RESPIRATION:  like volition, the motive influence in respiration
passes in a DIRECT LINE from one point of the nervous system to
certain muscles; but as voluntary motion seems to originate in
the cerebrum, so the respiratory motions originate in the medulla
oblongata: like the voluntary motions, the motions of
respirations are spontaneous; they continue, at least, after the
eighth pair of nerves have been divided.  The THIRD kind of
muscular action in the animal economy is that termed involuntary: 
it depends upon the principle of irritability and requires the
IMMEDIATE application of a stimulus to the nervo-muscular fibre
itself. These three kinds of muscular motion are well known to
physiologists; and I believe they are all which have been
hitherto pointed out. There is, however, a FOURTH, which
subsists, in part, after the voluntary and respiratory motions
have ceased, by the removal of the cerebrum and medulla
oblongata, and which is attached to the medulla spinalis, ceasing
itself when this is removed, and leaving the irritability
undiminished. In this kind of muscular motion the motive
influence does not originate in any central part of the nervous
system, but from a distance from that centre; it is neither
spontaneous in its action nor direct in its course; it is, on the
contrary, EXCITED by the application of appropriate stimuli,
which are not, however, applied immediately to the muscular or
nervo-muscular fibre, but to certain membraneous parts, whence
the impression is carried through the medulla, REFLECTED and
reconducted to the part impressed, or conducted to a part remote
from it in which muscular contraction is effected.

"The first three modes of muscular action are known only by
actual movements of muscular contractions.  But the reflex
function exists as a continuous muscular action, as a power
presiding over organs not actually in a state of motion,
preserving in some, as the glottis, an open, in others, as the
sphincters, a closed form, and in the limbs a due degree of
equilibrium or balanced muscular action--a function not, I think,
hitherto recognized by physiologists.

The three kinds of muscular motion hitherto known may be
distinguished in another way.  The muscles of voluntary motion
and of respiration may be excited by stimulating the nerves which
supply them, in any part of their course, whether at their source
as a part of the medulla oblongata or the medulla spinalis or
exterior to the spinal canal: the muscles of involuntary motion
are chiefly excited by the actual contact of stimuli.  In the
case of the reflex function alone the muscles are excited by a
stimulus acting mediately and indirectly in a curved and reflex
course, along superficial subcutaneous or submucous nerves
proceeding from the medulla. The first three of these causes of
muscular motion may act on detached limbs or muscles.  The last
requires the connection with the medulla to be preserved entire.

"All the kinds of muscular motion may be unduly excited, but the
reflex function is peculiar in being excitable in two modes of
action, not previously subsisting in the animal economy, as in
the case of sneezing, coughing, vomiting, etc. The reflex
function also admits of being permanently diminished or augmented
and of taking on some other morbid forms, of which I shall treat
hereafter.

"Before I proceed to the details of the experiments upon which
this disposition rests, it may be well to point out several
instances in illustration of the various sources of and the modes
of muscular action which have been enumerated. None can be more
familiar than the act of swallowing. Yet how complicated is the
act!  The apprehension of the food by the teeth and tongue, etc.,
is voluntary, and cannot, therefore, take place in an animal from
which the cerebrum is removed. The transition of food over the
glottis and along the middle and lower part of the pharynx
depends upon the reflex action: it can take place in animals from
which the cerebrum has been removed or the ninth pair of nerves
divided; but it requires the connection with the medulla
oblongata to be preserved entirely; and the actual contact of
some substance which may act as a stimulus:  it is attended by
the accurate closure of the glottis and by the contraction of the
pharynx. The completion of the act of deglutition is dependent
upon the stimulus immediately impressed upon the muscular fibre
of the oesophagus, and is the result of excited irritability.

"However plain these observations may have made the fact that
there is a function of the nervous muscular system distinct from
sensation, from the voluntary and respiratory motions, and from
irritability, it is right, in every such inquiry as the present,
that the statements and reasonings should be made with the
experiment, as it were, actually before us. It has already been
remarked that the voluntary and respiratory motions are
spontaneous, not necessarily requiring the agency of a stimulus.
If, then, an animal can be placed in such circumstances that such
motions will certainly not take place, the power of moving
remaining, it may be concluded that volition and the motive
influence of respiration are annihilated. Now this is effected by
removing the cerebrum and the medulla oblongata. These facts are
fully proved by the experiments of Legallois and M. Flourens, and
by several which I proceed to detail, for the sake of the
opportunity afforded by doing so of stating the arguments most
clearly.

"I divided the spinal marrow of a very lively snake between the
second and third vertebrae.  The movements of the animal were
immediately before extremely vigorous and unintermitted. From the
moment of the division of the spinal marrow it lay perfectly
tranquil and motionless, with the exception of occasional
gaspings and slight movements of the head. It became quite
evident that this state of quiescence would continue indefinitely
were the animal secured from all external impressions.

"Being now stimulated, the body began to move with great
activity, and continued to do so for a considerable time, each
change of position or situation bringing some fresh part of the
surface of the animal into contact with the table or other
objects and renewing the application of stimulants.

"At length the animal became again quiescent; and being carefully
protected from all external impressions it moved no more, but
died in the precise position and form which it had last assumed.

"It requires a little manoeuvre to perform this experiment
successfully: the motions of the animal must be watched and
slowly and cautiously arrested by opposing some soft substance,
as a glove or cotton wool; they are by this means gradually
lulled into quiescence. The slightest touch with a hard
substance, the slightest stimulus, will, on the other hand, renew
the movements on the animal in an active form. But that this
phenomenon does not depend upon sensation is further fully proved
by the facts that the position last assumed, and the stimuli, may
be such as would be attended by extreme or continued pain, if the
sensibility were undestroyed:  in one case the animal remained
partially suspended over the acute edge of the table; in others
the infliction of punctures and the application of a lighted
taper did not prevent the animal, still possessed of active
powers of motion, from passing into a state of complete and
permanent quiescence."


In summing up this long paper Hall concludes with this sentence:
"The reflex function appears in a word to be the COMPLEMENT of
the functions of the nervous system hitherto known."[2]

All these considerations as to nerve currents and nerve tracts
becoming stock knowledge of science, it was natural that interest
should become stimulated as to the exact character of these nerve
tracts in themselves, and all the more natural in that the
perfected microscope was just now claiming all fields for its
own. A troop of observers soon entered upon the study of the
nerves, and the leader here, as in so many other lines of
microscopical research, was no other than Theodor Schwann. 
Through his efforts, and with the invaluable aid of such other
workers as Remak, Purkinje, Henle, Muller, and the rest, all the
mystery as to the general characteristics of nerve tracts was
cleared away. It came to be known that in its essentials a nerve
tract is a tenuous fibre or thread of protoplasm stretching
between two terminal points in the organism, one of such termini
being usually a cell of the brain or spinal cord, the other a
distribution-point at or near the periphery--for example, in a
muscle or in the skin. Such a fibril may have about it a
protective covering, which is known as the sheath of Schwann; but
the fibril itself is the essential nerve tract; and in many
cases, as Remak presently discovered, the sheath is dispensed
with, particularly in case of the nerves of the so-called
sympathetic system.

This sympathetic system of ganglia and nerves, by-the-bye, had
long been a puzzle to the physiologists.  Its ganglia, the
seeming centre of the system, usually minute in size and never
very large, are found everywhere through the organism, but in
particular are gathered into a long double chain which lies
within the body cavity, outside the spinal column, and represents
the sole nervous system of the non-vertebrated organisms. Fibrils
from these ganglia were seen to join the cranial and spinal nerve
fibrils and to accompany them everywhere, but what special
function they subserved was long a mere matter of conjecture and
led to many absurd speculations.  Fact was not substituted for
conjecture until about the year 1851, when the great Frenchman
Claude Bernard conclusively proved that at least one chief
function of the sympathetic fibrils is to cause contraction of
the walls of the arterioles of the system, thus regulating the
blood-supply of any given part. Ten years earlier Henle had
demonstrated the existence of annular bands of muscle fibres in
the arterioles, hitherto a much-mooted question, and several
tentative explanations of the action of these fibres had been
made, particularly by the brothers Weber, by Stilling, who, as
early as 1840, had ventured to speak of "vaso-motor" nerves, and
by Schiff, who was hard upon the same track at the time of
Bernard's discovery. But a clear light was not thrown on the
subject until Bernard's experiments were made in 1851.  The
experiments were soon after confirmed and extended by
Brown-Sequard, Waller, Budge, and numerous others, and henceforth
physiologists felt that they understood how the blood-supply of
any given part is regulated by the nervous system.

In reality, however, they had learned only half the story, as
Bernard himself proved only a few years later by opening up a new
and quite unsuspected chapter.  While experimenting in 1858 he
discovered that there are certain nerves supplying the heart
which, if stimulated, cause that organ to relax and cease
beating.  As the heart is essentially nothing more than an
aggregation of muscles, this phenomenon was utterly puzzling and
without precedent in the experience of physiologists. An impulse
travelling along a motor nerve had been supposed to be able to
cause a muscular contraction and to do nothing else; yet here
such an impulse had exactly the opposite effect. The only tenable
explanation seemed to be that this particular impulse must arrest
or inhibit the action of the impulses that ordinarily cause the
heart muscles to contract. But the idea of such inhibition of one
impulse by another was utterly novel and at first difficult to
comprehend. Gradually, however, the idea took its place in the
current knowledge of nerve physiology, and in time it came to be
understood that what happens in the case of the heart
nerve-supply is only a particular case under a very general,
indeed universal, form of nervous action.  Growing out of
Bernard's initial discovery came the final understanding that the
entire nervous system is a mechanism of centres subordinate and
centres superior, the action of the one of which may be
counteracted and annulled in effect by the action of the other. 
This applies not merely to such physical processes as heart-beats
and arterial contraction and relaxing, but to the most intricate
functionings which have their counterpart in psychical processes
as well. Thus the observation of the inhibition of the heart's
action by a nervous impulse furnished the point of departure for
studies that led to a better understanding of the modus operandi
of the mind's activities than had ever previously been attained
by the most subtle of psychologists.


PSYCHO-PHYSICS

The work of the nerve physiologists had thus an important bearing
on questions of the mind.  But there was another company of
workers of this period who made an even more direct assault upon
the "citadel of thought." A remarkable school of workers had been
developed in Germany, the leaders being men who, having more or
less of innate metaphysical bias as a national birthright, had
also the instincts of the empirical scientist, and whose
educational equipment included a profound knowledge not alone of
physiology and psychology, but of physics and mathematics as
well. These men undertook the novel task of interrogating the
relations of body and mind from the standpoint of physics.  They
sought to apply the vernier and the balance, as far as might be,
to the intangible processes of mind.

The movement had its precursory stages in the early part of the
century, notably in the mathematical psychology of Herbart, but
its first definite output to attract general attention came from
the master-hand of Hermann Helmholtz in 1851. It consisted of the
accurate measurement of the speed of transit of a nervous impulse
along a nerve tract.  To make such measurement had been regarded
as impossible, it being supposed that the flight of the nervous
impulse was practically instantaneous. But Helmholtz readily
demonstrated the contrary, showing that the nerve cord is a
relatively sluggish message-bearer. According to his experiments,
first performed upon the frog, the nervous "current" travels less
than one hundred feet per second. Other experiments performed
soon afterwards by Helmholtz himself, and by various followers,
chief among whom was Du Bois-Reymond, modified somewhat the exact
figures at first obtained, but did not change the general
bearings of the early results. Thus the nervous impulse was shown
to be something far different, as regards speed of transit, at
any rate, from the electric current to which it had been so often
likened. An electric current would flash halfway round the globe
while a nervous impulse could travel the length of the human
body--from a man's foot to his brain.

The tendency to bridge the gulf that hitherto had separated the
physical from the psychical world was further evidenced in the
following decade by Helmholtz's remarkable but highly technical
study of the sensations of sound and of color in connection with
their physical causes, in the course of which he revived the
doctrine of color vision which that other great physiologist and
physicist, Thomas Young, had advanced half a century before. The
same tendency was further evidenced by the appearance, in 1852,
of Dr. Hermann Lotze's famous Medizinische Psychologie, oder
Physiologie der Seele, with its challenge of the old myth of a
"vital force."  But the most definite expression of the new
movement was signalized in 1860, when Gustav Fechner published
his classical work called Psychophysik.  That title introduced a
new word into the vocabulary of science. Fechner explained it by
saying, "I mean by psychophysics an exact theory of the relation
between spirit and body, and, in a general way, between the
physical and the psychic worlds." The title became famous and the
brunt of many a controversy. So also did another phrase which
Fechner introduced in the course of his book--the phrase
"physiological psychology." In making that happy collocation of
words Fechner virtually christened a new science.


FECHNER EXPOUNDS WEBER'S LAW

The chief purport of this classical book of the German
psycho-physiologist was the elaboration and explication of
experiments based on a method introduced more than twenty years
earlier by his countryman E. H. Weber, but which hitherto had
failed to attract the attention it deserved. The method consisted
of the measurement and analysis of the definite relation existing
between external stimuli of varying degrees of intensity (various
sounds, for example) and the mental states they induce. Weber's
experiments grew out of the familiar observation that the nicety
of our discriminations of various sounds, weights, or visual
images depends upon the magnitude of each particular cause of a
sensation in its relation with other similar causes.  Thus, for
example, we cannot see the stars in the daytime, though they
shine as brightly then as at night. Again, we seldom notice the
ticking of a clock in the daytime, though it may become almost
painfully audible in the silence of the night. Yet again, the
difference between an ounce weight and a two-ounce weight is
clearly enough appreciable when we lift the two, but one cannot
discriminate in the same way between a five-pound weight and a
weight of one ounce over five pounds.

This last example, and similar ones for the other senses, gave
Weber the clew to his novel experiments.  Reflection upon
every-day experiences made it clear to him that whenever we
consider two visual sensations, or two auditory sensations, or
two sensations of weight, in comparison one with another, there
is always a limit to the keenness of our discrimination, and that
this degree of keenness varies, as in the case of the weights
just cited, with the magnitude of the exciting cause.

Weber determined to see whether these common experiences could be
brought within the pale of a general law. His method consisted of
making long series of experiments aimed at the determination, in
each case, of what came to be spoken of as the least observable
difference between the stimuli. Thus if one holds an ounce weight
in each hand, and has tiny weights added to one of them, grain by
grain, one does not at first perceive a difference; but
presently, on the addition of a certain grain, he does become
aware of the difference. Noting now how many grains have been
added to produce this effect, we have the weight which represents
the least appreciable difference when the standard is one ounce.

Now repeat the experiment, but let the weights be each of five
pounds. Clearly in this case we shall be obliged to add not
grains, but drachms, before a difference between the two heavy
weights is perceived.  But whatever the exact amount added, that
amount represents the stimulus producing a just-perceivable
sensation of difference when the standard is five pounds. And so
on for indefinite series of weights of varying magnitudes. Now
came Weber's curious discovery.  Not only did he find that in
repeated experiments with the same pair of weights the measure of
"just-{p}erceivable difference" remained approximately fixed, but
he found, further, that a remarkable fixed relation exists
between the stimuli of different magnitude.  If, for example, he
had found it necessary, in the case of the ounce weights, to add
one-fiftieth of an ounce to the one before a difference was
detected, he found also, in the case of the five-pound weights,
that one-fiftieth of five pounds must be added before producing
the same result.  And so of all other weights; the amount added
to produce the stimulus of "least-appreciable difference" always
bore the same mathematical relation to the magnitude of the
weight used, be that magnitude great or small.

Weber found that the same thing holds good for the stimuli of the
sensations of sight and of hearing, the differential stimulus
bearing always a fixed ratio to the total magnitude of the
stimuli. Here, then, was the law he had sought.

Weber's results were definite enough and striking enough, yet
they failed to attract any considerable measure of attention
until they were revived and extended by Fechner and brought
before the world in the famous work on psycho-physics. Then they
precipitated a veritable melee. Fechner had not alone verified
the earlier results (with certain limitations not essential to
the present consideration), but had invented new methods of
making similar tests, and had reduced the whole question to
mathematical treatment.  He pronounced Weber's discovery the
fundamental law of psycho-physics. In honor of the discoverer, he
christened it Weber's Law.  He clothed the law in words and in
mathematical formulae, and, so to say, launched it full tilt at
the heads of the psychological world.  It made a fine commotion,
be assured, for it was the first widely heralded bulletin of the
new psychology in its march upon the strongholds of the
time-honored metaphysics. The accomplishments of the
microscopists and the nerve physiologists had been but
preliminary--mere border skirmishes of uncertain import. But here
was proof that the iconoclastic movement meant to invade the very
heart of the sacred territory of mind--a territory from which
tangible objective fact had been supposed to be forever barred.


PHYSIOLOGICAL PSYCHOLOGY

Hardly had the alarm been sounded, however, before a new movement
was made.  While Fechner's book was fresh from the press, steps
were being taken to extend the methods of the physicist in yet
another way to the intimate processes of the mind. As Helmholtz
had shown the rate of nervous impulsion along the nerve tract to
be measurable, it was now sought to measure also the time
required for the central nervous mechanism to perform its work of
receiving a message and sending out a response. This was coming
down to the very threshold of mind. The attempt was first made by
Professor Donders in 1861, but definitive results were only
obtained after many years of experiment on the part of a host of
observers. The chief of these, and the man who has stood in the
forefront of the new movement and has been its recognized leader
throughout the remainder of the century, is Dr. Wilhelm Wundt, of
Leipzig.

The task was not easy, but, in the long run, it was accomplished.
Not alone was it shown that the nerve centre requires a
measurable time for its operations, but much was learned as to
conditions that modify this time.  Thus it was found that
different persons vary in the rate of their central nervous
activity--which explained the "personal equation" that the
astronomer Bessel had noted a half-century before. It was found,
too, that the rate of activity varies also for the same person
under different conditions, becoming retarded, for example, under
influence of fatigue, or in case of certain diseases of the
brain.  All details aside, the essential fact emerges, as an
experimental demonstration, that the intellectual
processes--sensation, apperception, volition--are linked
irrevocably with the activities of the central nervous tissues,
and that these activities, like all other physical processes,
have a time element.  To that old school of psychologists, who
scarcely cared more for the human head than for the heels--being
interested only in the mind--such a linking of mind and body as
was thus demonstrated was naturally disquieting. But whatever the
inferences, there was no escaping the facts.

Of course this new movement has not been confined to Germany. 
Indeed, it had long had exponents elsewhere. Thus in England, a
full century earlier, Dr. Hartley had championed the theory of
the close and indissoluble dependence of the mind upon the brain,
and formulated a famous vibration theory of association that
still merits careful consideration. Then, too, in France, at the
beginning of the century, there was Dr. Cabanis with his
tangible, if crudely phrased, doctrine that the brain digests
impressions and secretes thought as the stomach digests food and
the liver secretes bile. Moreover, Herbert Spencer's Principles
of Psychology, with its avowed co-ordination of mind and body and
its vitalizing theory of evolution, appeared in 1855, half a
decade before the work of Fechner.  But these influences, though
of vast educational value, were theoretical rather than
demonstrative, and the fact remains that the experimental work
which first attempted to gauge mental operations by physical
principles was mainly done in Germany.  Wundt's Physiological
Psychology, with its full preliminary descriptions of the anatomy
of the nervous system, gave tangible expression to the growth of
the new movement in 1874; and four years later, with the opening
of his laboratory of physiological psychology at the University
of Leipzig, the new psychology may be said to have gained a
permanent foothold and to have forced itself into official
recognition. From then on its conquest of the world was but a
matter of time.

It should be noted, however, that there is one other method of
strictly experimental examination of the mental field, latterly
much in vogue, which had a different origin. This is the
scientific investigation of the phenomena of hypnotism. This
subject was rescued from the hands of charlatans, rechristened,
and subjected to accurate investigation by Dr. James Braid, of
Manchester, as early as 1841. But his results, after attracting
momentary attention, fell from view, and, despite desultory
efforts, the subject was not again accorded a general hearing
from the scientific world until 1878, when Dr. Charcot took it up
at the Salpetriere, in Paris, followed soon afterwards by Dr.
Rudolf Heidenhain, of Breslau, and a host of other experimenters. 
The value of the method in the study of mental states was soon
apparent. Most of Braid's experiments were repeated, and in the
main his results were confirmed.  His explanation of hypnotism,
or artificial somnambulism, as a self-induced state, independent
of any occult or supersensible influence, soon gained general
credence.  His belief that the initial stages are due to fatigue
of nervous centres, usually from excessive stimulation, has not
been supplanted, though supplemented by notions growing out of
the new knowledge as to subconscious mentality in general, and
the inhibitory influence of one centre over another in the
central nervous mechanism.


THE BRAIN AS THE ORGAN OF MIND

These studies of the psychologists and pathologists bring the
relations of mind and body into sharp relief.  But even more
definite in this regard was the work of the brain physiologists.
Chief of these, during the middle period of the century, was the
man who is sometimes spoken of as the "father of brain
physiology," Marie Jean Pierre Flourens, of the Jardin des
Plantes of Paris, the pupil and worthy successor of Magendie. 
His experiments in nerve physiology were begun in the first
quarter of the century, but his local experiments upon the brain
itself were not culminated until about 1842. At this time the old
dispute over phrenology had broken out afresh, and the studies of
Flourens were aimed, in part at least, at the strictly scientific
investigation of this troublesome topic.

In the course of these studies Flourens discovered that in the
medulla oblongata, the part of the brain which connects that
organ with the spinal cord, there is a centre of minute size
which cannot be injured in the least without causing the instant
death of the animal operated upon.  It may be added that it is
this spot which is reached by the needle of the garroter in
Spanish executions, and that the same centre also is destroyed
when a criminal is "successfully" hanged, this time by the forced
intrusion of a process of the second cervical vertebra. Flourens
named this spot the "vital knot."  Its extreme importance, as is
now understood, is due to the fact that it is the centre of
nerves that supply the heart; but this simple explanation,
annulling the conception of a specific "life centre," was not at
once apparent.

Other experiments of Flourens seemed to show that the cerebellum
is the seat of the centres that co-ordinate muscular activities,
and that the higher intellectual faculties are relegated to the
cerebrum. But beyond this, as regards localization, experiment
faltered. Negative results, as regards specific faculties, were
obtained from all localized irritations of the cerebrum, and
Flourens was forced to conclude that the cerebral lobe, while
being undoubtedly the seat of higher intellection, performs its
functions with its entire structure. This conclusion, which
incidentally gave a quietus to phrenology, was accepted
generally, and became the stock doctrine of cerebral physiology
for a generation.

It will be seen, however, that these studies of Flourens had a
double bearing.  They denied localization of cerebral functions,
but they demonstrated the localization of certain nervous
processes in other portions of the brain.  On the whole, then,
they spoke positively for the principle of localization of
function in the brain, for which a certain number of students
contended; while their evidence against cerebral localization was
only negative. There was here and there an observer who felt that
this negative testimony was not conclusive.  In particular, the
German anatomist Meynert, who had studied the disposition of
nerve tracts in the cerebrum, was led to believe that the
anterior portions of the cerebrum must have motor functions in
preponderance; the posterior positions, sensory functions. 
Somewhat similar conclusions were reached also by Dr.
Hughlings-Jackson, in England, from his studies of epilepsy. But
no positive evidence was forthcoming until 1861, when Dr. Paul
Broca brought before the Academy of Medicine in Paris a case of
brain lesion which he regarded as having most important bearings
on the question of cerebral localization.

The case was that of a patient at the Bicetre, who for twenty
years had been deprived of the power of speech, seemingly through
loss of memory of words. In 1861 this patient died, and an
autopsy revealed that a certain convolution of the left frontal
lobe of his cerebrum had been totally destroyed by disease, the
remainder of his brain being intact. Broca felt that this
observation pointed strongly to a localization of the memory of
words in a definite area of the brain.  Moreover, it transpired
that the case was not without precedent.  As long ago as 1825 Dr.
Boillard had been led, through pathological studies, to locate
definitely a centre for the articulation of words in the frontal
lobe, and here and there other observers had made tentatives in
the same direction. Boillard had even followed the matter up with
pertinacity, but the world was not ready to listen to him.  Now,
however, in the half-decade that followed Broca's announcements,
interest rose to fever-beat, and through the efforts of Broca,
Boillard, and numerous others it was proved that a veritable
centre having a strange domination over the memory of articulate
words has its seat in the third convolution of the frontal lobe
of the cerebrum, usually in the left hemisphere. That part of the
brain has since been known to the English-speaking world as the
convolution of Broca, a name which, strangely enough, the
discoverer's compatriots have been slow to accept.

This discovery very naturally reopened the entire subject of
brain localization.  It was but a short step to the inference
that there must be other definite centres worth the seeking, and
various observers set about searching for them.  In 1867 a clew
was gained by Eckhard, who, repeating a forgotten experiment by
Haller and Zinn of the previous century, removed portions of the
brain cortex of animals, with the result of producing
convulsions. But the really vital departure was made in 1870 by
the German investigators Fritsch and Hitzig, who, by stimulating
definite areas of the cortex of animals with a galvanic current,
produced contraction of definite sets of muscles of the opposite
side of the body. These most important experiments, received at
first with incredulity, were repeated and extended in 1873 by Dr.
David Ferrier, of London, and soon afterwards by a small army of
independent workers everywhere, prominent among whom were Franck
and Pitres in France, Munck and Goltz in Germany, and Horsley and
Schafer in England.  The detailed results, naturally enough, were
not at first all in harmony.  Some observers, as Goltz, even
denied the validity of the conclusions in toto. But a consensus
of opinion, based on multitudes of experiments, soon placed the
broad general facts for which Fritsch and Hitzig contended beyond
controversy.  It was found, indeed, that the cerebral centres of
motor activities have not quite the finality at first ascribed to
them by some observers, since it may often happen that after the
destruction of a centre, with attending loss of function, there
may be a gradual restoration of the lost function, proving that
other centres have acquired the capacity to take the place of the
one destroyed.  There are limits to this capacity for
substitution, however, and with this qualification the
definiteness of the localization of motor functions in the
cerebral cortex has become an accepted part of brain physiology.

Nor is such localization confined to motor centres. Later
experiments, particularly of Ferrier and of Munck, proved that
the centres of vision are equally restricted in their location,
this time in the posterior lobes of the brain, and that hearing
has likewise its local habitation. Indeed, there is every reason
to believe that each form of primary sensation is based on
impressions which mainly come to a definitely localized goal in
the brain.  But all this, be it understood, has no reference to
the higher forms of intellection. All experiment has proved
futile to localize these functions, except indeed to the extent
of corroborating the familiar fact of their dependence upon the
brain, and, somewhat problematically, upon the anterior lobes of
the cerebrum in particular. But this is precisely what should be
expected, for the clearer insight into the nature of mental
processes makes it plain that in the main these alleged
"faculties" are not in themselves localized. Thus, for example,
the "faculty" of language is associated irrevocably with centres
of vision, of hearing, and of muscular activity, to go no
further, and only becomes possible through the association of
these widely separated centres. The destruction of Broca's
centre, as was early discovered, does not altogether deprive a
patient of his knowledge of language. He may be totally unable to
speak (though as to this there are all degrees of variation), and
yet may comprehend what is said to him, and be able to read,
think, and even write correctly. Thus it appears that Broca's
centre is peculiarly bound up with the capacity for articulate
speech, but is far enough from being the seat of the faculty of
language in its entirety.

In a similar way, most of the supposed isolated "faculties" of
higher intellection appear, upon clearer analysis, as complex
aggregations of primary sensations, and hence necessarily
dependent upon numerous and scattered centres. Some "faculties,"
as memory and volition, may be said in a sense to be primordial
endowments of every nerve cell--even of every body cell.  Indeed,
an ultimate analysis relegates all intellection, in its
primordial adumbrations, to every particle of living matter. But
such refinements of analysis, after all, cannot hide the fact
that certain forms of higher intellection involve a pretty
definite collocation and elaboration of special sensations. Such
specialization, indeed, seems a necessary accompaniment of mental
evolution.  That every such specialized function has its
localized centres of co-ordination, of some such significance as
the demonstrated centres of articulate speech, can hardly be in
doubt--though this, be it understood, is an induction, not as yet
a demonstration.  In other words, there is every reason to
believe that numerous "centres," in this restricted sense, exist
in the brain that have as yet eluded the investigator. Indeed,
the current conception regards the entire cerebral cortex as
chiefly composed of centres of ultimate co-ordination of
impressions, which in their cruder form are received by more
primitive nervous tissues--the basal ganglia, the cerebellum and
medulla, and the spinal cord.

This, of course, is equivalent to postulating the cerebral cortex
as the exclusive seat of higher intellection. This proposition,
however, to which a safe induction seems to lead, is far afield
from the substantiation of the old conception of brain
localization, which was based on faulty psychology and equally
faulty inductions from few premises. The details of Gall's
system, as propounded by generations of his mostly unworthy
followers, lie quite beyond the pale of scientific discussion. 
Yet, as I have said, a germ of truth was there--the idea of
specialization of cerebral functions--and modern investigators
have rescued that central conception from the phrenological
rubbish heap in which its discoverer unfortunately left it
buried.


THE MINUTE STRUCTURE OF THE BRAIN

The common ground of all these various lines of investigations of
pathologist, anatomist, physiologist, physicist, and psychologist
is, clearly, the central nervous system--the spinal cord and the
brain. The importance of these structures as the foci of nervous
and mental activities has been recognized more and more with each
new accretion of knowledge, and the efforts to fathom the secrets
of their intimate structure has been unceasing. For the earlier
students, only the crude methods of gross dissections and
microscopical inspection were available. These could reveal
something, but of course the inner secrets were for the keener
insight of the microscopist alone. And even for him the task of
investigation was far from facile, for the central nervous
tissues are the most delicate and fragile, and on many accounts
the most difficult of manipulation of any in the body.

Special methods, therefore, were needed for this essay, and brain
histology has progressed by fitful impulses, each forward jet
marking the introduction of some ingenious improvement of
mechanical technique, which placed a new weapon in the hands of
the investigators.

The very beginning was made in 1824 by Rolando, who first thought
of cutting chemically hardened pieces of brain tissues into thin
sections for microscopical examination--the basal structure upon
which almost all the later advances have been conducted. Muller
presently discovered that bichromate of potassium in solution
makes the best of fluids for the preliminary preservation and
hardening of the tissues.  Stilling, in 1842, perfected the
method by introducing the custom of cutting a series of
consecutive sections of the same tissue, in order to trace nerve
tracts and establish spacial relations.  Then from time to time
mechanical ingenuity added fresh details of improvement. It was
found that pieces of hardened tissue of extreme delicacy can be
made better subject to manipulation by being impregnated with
collodion or celloidine and embedded in paraffine. Latterly it
has become usual to cut sections also from fresh tissues,
unchanged by chemicals, by freezing them suddenly with vaporized
ether or, better, carbonic acid. By these methods, and with the
aid of perfected microtomes, the worker of recent periods avails
himself of sections of brain tissues of a tenuousness which the
early investigators could not approach.

But more important even than the cutting of thin sections is the
process of making the different parts of the section visible, one
tissue differentiated from another.  The thin section, as the
early workers examined it, was practically colorless, and even
the crudest details of its structure were made out with extreme
difficulty.  Remak did, indeed, manage to discover that the brain
tissue is cellular, as early as 1833, and Ehrenberg in the same
year saw that it is also fibrillar, but beyond this no great
advance was made until 1858, when a sudden impulse was received
from a new process introduced by Gerlach.  The process itself was
most simple, consisting essentially of nothing more than the
treatment of a microscopical section with a solution of carmine.
But the result was wonderful, for when such a section was placed
under the lens it no longer appeared homogeneous. Sprinkled
through its substance were seen irregular bodies that had taken
on a beautiful color, while the matrix in which they were
embedded remained unstained.  In a word, the central nerve cell
had sprung suddenly into clear view.

A most interesting body it proved, this nerve cell, or ganglion
cell, as it came to be called.  It was seen to be exceedingly
minute in size, requiring high powers of the microscope to make
it visible. It exists in almost infinite numbers, not, however,
scattered at random through the brain and spinal cord.  On the
contrary, it is confined to those portions of the central nervous
masses which to the naked eye appear gray in color, being
altogether wanting in the white substance which makes up the
chief mass of the brain. Even in the gray matter, though
sometimes thickly distributed, the ganglion cells are never in
actual contact one with another; they always lie embedded in
intercellular tissues, which came to be known, following Virchow,
as the neuroglia.

Each ganglion cell was seen to be irregular in contour, and to
have jutting out from it two sets of minute fibres, one set
relatively short, indefinitely numerous, and branching in every
direction; the other set limited in number, sometimes even
single, and starting out directly from the cell as if bent on a
longer journey. The numerous filaments came to be known as
protoplasmic processes; the other fibre was named, after its
discoverer, the axis cylinder of Deiters.  It was a natural
inference, though not clearly demonstrable in the sections, that
these filamentous processes are the connecting links between the
different nerve cells and also the channels of communication
between nerve cells and the periphery of the body. The white
substance of brain and cord, apparently, is made up of such
connecting fibres, thus bringing the different ganglion cells
everywhere into communication one with another.

In the attempt to trace the connecting nerve tracts through this
white substance by either macroscopical or microscopical methods,
most important aid is given by a method originated by Waller in
1852. Earlier than that, in 1839, Nasse had discovered that a
severed nerve cord degenerates in its peripheral portions. Waller
discovered that every nerve fibre, sensory or motor, has a nerve
cell to or from which it leads, which dominates its nutrition, so
that it can only retain its vitality while its connection with
that cell is intact.  Such cells he named trophic centres.
Certain cells of the anterior part of the spinal cord, for
example, are the trophic centres of the spinal motor nerves.
Other trophic centres, governing nerve tracts in the spinal cord
itself, are in the various regions of the brain. It occurred to
Waller that by destroying such centres, or by severing the
connection at various regions between a nervous tract and its
trophic centre, sharply defined tracts could be made to
degenerate, and their location could subsequently be accurately
defined, as the degenerated tissues take on a changed aspect,
both to macroscopical and microscopical observation. Recognition
of this principle thus gave the experimenter a new weapon of
great efficiency in tracing nervous connections. Moreover, the
same principle has wide application in case of the human subject
in disease, such as the lesion of nerve tracts or the destruction
of centres by localized tumors, by embolisms, or by traumatisms.

All these various methods of anatomical examination combine to
make the conclusion almost unavoidable that the central ganglion
cells are the veritable "centres" of nervous activity to which so
many other lines of research have pointed. The conclusion was
strengthened by experiments of the students of motor
localization, which showed that the veritable centres of their
discovery lie, demonstrably, in the gray cortex of the brain, not
in the white matter.  But the full proof came from pathology. At
the hands of a multitude of observers it was shown that in
certain well-known diseases of the spinal cord, with resulting
paralysis, it is the ganglion cells themselves that are found to
be destroyed. Similarly, in the case of sufferers from chronic
insanities, with marked dementia, the ganglion cells of the
cortex of the brain are found to have undergone degeneration. The
brains of paretics in particular show such degeneration, in
striking correspondence with their mental decadence. The position
of the ganglion cell as the ultimate centre of nervous activities
was thus placed beyond dispute.

Meantime, general acceptance being given the histological scheme
of Gerlach, according to which the mass of the white substance of
the brain is a mesh-work of intercellular fibrils, a proximal
idea seemed attainable of the way in which the ganglionic
activities are correlated, and, through association, built up, so
to speak, into the higher mental processes. Such a conception
accorded beautifully with the ideas of the associationists, who
had now become dominant in psychology. But one standing puzzle
attended this otherwise satisfactory correlation of anatomical
observations and psychic analyses. It was this:  Since, according
to the histologist, the intercellular fibres, along which
impulses are conveyed, connect each brain cell, directly or
indirectly, with every other brain cell in an endless mesh-work,
how is it possible that various sets of cells may at times be
shut off from one another? Such isolation must take place, for
all normal ideation depends for its integrity quite as much upon
the shutting-out of the great mass of associations as upon the
inclusion of certain other associations. For example, a student
in solving a mathematical problem must for the moment become
quite oblivious to the special associations that have to do with
geography, natural history, and the like. But does histology give
any clew to the way in which such isolation may be effected?

Attempts were made to find an answer through consideration of the
very peculiar character of the blood-supply in the brain. Here,
as nowhere else, the terminal twigs of the arteries are arranged
in closed systems, not anastomosing freely with neighboring
systems. Clearly, then, a restricted area of the brain may,
through the controlling influence of the vasomotor nerves, be
flushed with arterial blood while neighboring parts remain
relatively anaemic. And since vital activities unquestionably
depend in part upon the supply of arterial blood, this peculiar
arrangement of the vascular mechanism may very properly be
supposed to aid in the localized activities of the central
nervous ganglia. But this explanation left much to be desired--in
particular when it is recalled that all higher intellection must
in all probability involve multitudes of widely scattered
centres.

No better explanation was forthcoming, however, until the year
1889, when of a sudden the mystery was cleared away by a fresh
discovery. Not long before this the Italian histologist Dr.
Camille Golgi had discovered a method of impregnating hardened
brain tissues with a solution of nitrate of silver, with the
result of staining the nerve cells and their processes almost
infinitely better than was possible by the methods of Gerlach, or
by any of the multiform methods that other workers had
introduced. Now for the first time it became possible to trace
the cellular prolongations definitely to their termini, for the
finer fibrils had not been rendered visible by any previous
method of treatment. Golgi himself proved that the set of fibrils
known as protoplasmic prolongations terminate by free
extremities, and have no direct connection with any cell save the
one from which they spring. He showed also that the axis
cylinders give off multitudes of lateral branches not hitherto
suspected.  But here he paused, missing the real import of the
discovery of which he was hard on the track.  It remained for the
Spanish histologist Dr. S. Ramon y Cajal to follow up the
investigation by means of an improved application of Golgi's
method of staining, and to demonstrate that the axis cylinders,
together with all their collateral branches, though sometimes
extending to a great distance, yet finally terminate, like the
other cell prolongations, in arborescent fibrils having free
extremities.  In a word, it was shown that each central nerve
cell, with its fibrillar offshoots, is an isolated entity.
Instead of being in physical connection with a multitude of other
nerve cells, it has no direct physical connection with any other
nerve cell whatever.

When Dr. Cajal announced his discovery, in 1889, his
revolutionary claims not unnaturally amazed the mass of
histologists.  There were some few of them, however, who were not
quite unprepared for the revelation; in particular His, who had
half suspected the independence of the cells, because they seemed
to develop from dissociated centres; and Forel, who based a
similar suspicion on the fact that he had never been able
actually to trace a fibre from one cell to another. These
observers then came readily to repeat Cajal's experiments. So
also did the veteran histologist Kolliker, and soon afterwards
all the leaders everywhere.  The result was a practically
unanimous confirmation of the Spanish histologist's claims, and
within a few months after his announcements the old theory of
union of nerve cells into an endless mesh-work was completely
discarded, and the theory of isolated nerve elements--the theory
of neurons, as it came to be called--was fully established in its
place.

As to how these isolated nerve cells functionate, Dr. Cajal gave
the clew from the very first, and his explanation has met with
universal approval.

In the modified view, the nerve cell retains its old position as
the storehouse of nervous energy.  Each of the filaments jutting
out from the cell is held, as before, to be indeed a transmitter
of impulses, but a transmitter that operates intermittently, like
a telephone wire that is not always "connected," and, like that
wire, the nerve fibril operates by contact and not by continuity. 
Under proper stimulation the ends of the fibrils reach out, come
in contact with other end fibrils of other cells, and conduct
their destined impulse.  Again they retract, and communication
ceases for the time between those particular cells. Meantime, by
a different arrangement of the various conductors, different sets
of cells are placed in communication, different associations of
nervous impulses induced, different trains of thought engendered.
Each fibril when retracted becomes a non-conductor, but when
extended and in contact with another fibril, or with the body of
another cell, it conducts its message as readily as a continuous
filament could do--precisely as in the case of an electric wire.

This conception, founded on a most tangible anatomical basis,
enables us to answer the question as to how ideas are isolated,
and also, as Dr. Cajal points out, throws new light on many other
mental processes.  One can imagine, for example, by keeping in
mind the flexible nerve prolongations, how new trains of thought
may be engendered through novel associations of cells; how
facility of thought or of action in certain directions is
acquired through the habitual making of certain nerve-cell
connections; how certain bits of knowledge may escape our memory
and refuse to be found for a time because of a temporary
incapacity of the nerve cells to make the proper connections, and
so on indefinitely.

If one likens each nerve cell to a central telephone office, each
of its filamentous prolongations to a telephone wire, one can
imagine a striking analogy between the modus operandi of nervous
processes and of the telephone system. The utility of new
connections at the central office, the uselessness of the
mechanism when the connections cannot be made, the "wires in use"
that retard your message, perhaps even the crossing of wires,
bringing you a jangle of sounds far different from what you
desire--all these and a multiplicity of other things that will
suggest themselves to every user of the telephone may be imagined
as being almost ludicrously paralleled in the operations of the
nervous mechanism. And that parallel, startling as it may seem,
is not a mere futile imagining.  It is sustained and rendered
plausible by a sound substratum of knowledge of the anatomical
conditions under which the central nervous mechanism exists, and
in default of which, as pathology demonstrates with no less
certitude, its functionings are futile to produce the normal
manifestations of higher intellection.



X. THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY

HOW THE "RIDDLE OF THE SPHINX" WAS READ

Conspicuously placed in the great hall of Egyptian antiquities in
the British Museum is a wonderful piece of sculpture known as the
Rosetta Stone.  I doubt if any other piece in the entire exhibit
attracts so much attention from the casual visitor as this slab
of black basalt on its telescope-like pedestal.  The hall itself,
despite its profusion of strangely sculptured treasures, is never
crowded, but before this stone you may almost always find some
one standing, gazing with more or less of discernment at the
strange characters that are graven neatly across its upturned,
glass-protected face. A glance at this graven surface suffices to
show that three sets of inscriptions are recorded there.  The
upper one, occupying about one-fourth of the surface, is a
pictured scroll, made up of chains of those strange outlines of
serpents, hawks, lions, and so on, which are recognized, even by
the least initiated, as hieroglyphics. The middle inscription,
made up of lines, angles, and half-pictures, one might surmise to
be a sort of abbreviated or short-hand hieroglyphic. The third or
lower inscription is Greek--obviously a thing of words. If the
screeds above be also made of words, only the elect have any way
of proving the fact.

Fortunately, however, even the least scholarly observer is left
in no doubt as to the real import of the thing he sees, for an
obliging English label tells us that these three inscriptions are
renderings of the same message, and that this message is a
"decree of the priests of Memphis conferring divine honors on
Ptolemy V. (Epiphenes), King of Egypt, B.C. 195." The label goes
on to state that the upper inscription (of which, unfortunately,
only part of the last dozen lines or so remains, the slab being
broken) is in "the Egyptian language, in hieroglyphics, or
writing of the priests"; the second inscription "in the same
language is in Demotic, or the writing of the people"; and the
third "the Greek language and character."  Following this is a
brief biography of the Rosetta Stone itself, as follows: "The
stone was found by the French in 1798 among the ruins of Fort
Saint Julien, near the Rosetta mouth of the Nile.  It passed into
the hands of the British by the treaty of Alexandria, and was
deposited in the British Museum in the year 1801." There is a
whole volume of history in that brief inscription--and a bitter
sting thrown in, if the reader chance to be a Frenchman.  Yet the
facts involved could scarcely be suggested more modestly.  They
are recorded much more bluntly in a graven inscription on the
side of the stone, which reads: "Captured in Egypt by the British
Army, 1801." No Frenchman could read those words without a
veritable sinking of the heart.

The value of the Rosetta Stone depended on the fact that it gave
promise, even when casually inspected, of furnishing a key to the
centuries-old mystery of the hieroglyphics.  For two thousand
years the secret of these strange markings had been forgotten.
Nowhere in the world--quite as little in Egypt as elsewhere--had
any man the slightest clew to their meaning; there were those who
even doubted whether these droll picturings really had any
specific meaning, questioning whether they were not rather vague
symbols of esoteric religious import and nothing more. And it was
the Rosetta Stone that gave the answer to these doubters and
restored to the world a lost language and a forgotten literature.

The trustees of the museum recognized at once that the problem of
the Rosetta Stone was one on which the scientists of the world
might well exhaust their ingenuity, and promptly published to the
world a carefully lithographed copy of the entire inscription, so
that foreign scholarship had equal opportunity with the British
to try at the riddle. It was an Englishman, however, who first
gained a clew to the solution. This was none other than the
extraordinary Dr. Thomas Young, the demonstrator of the vibratory
nature of light.

Young's specific discoveries were these: (1) That many of the
pictures of the hieroglyphics stand for the names of the objects
actually delineated; (2) that other pictures are sometimes only
symbolic; (3) that plural numbers are represented by repetition;
(4) that numerals are represented by dashes; (5) that
hieroglyphics may read either from the right or from the left,
but always from the direction in which the animal and human
figures face; (6) that proper names are surrounded by a graven
oval ring, making what he called a cartouche; (7) that the
cartouches of the preserved portion of the Rosetta Stone stand
for the name of Ptolemy alone; (8) that the presence of a female
figure after such cartouches in other inscriptions always denotes
the female sex; (9) that within the cartouches the hieroglyphic
symbols have a positively phonetic value, either alphabetic or
syllabic; and (10) that several different characters may have the
same phonetic value.

Just what these phonetic values are Young pointed out in the case
of fourteen characters representing nine sounds, six of which are
accepted to-day as correctly representing the letters to which he
ascribed them, and the three others as being correct regarding
their essential or consonant element. It is clear, therefore,
that he was on the right track thus far, and on the very verge of
complete discovery.  But, unfortunately, he failed to take the
next step, which would have been to realize that the same
phonetic values which were given to the alphabetic characters
within the cartouches were often ascribed to them also when used
in the general text of an inscription; in other words, that the
use of an alphabet was not confined to proper names. This was the
great secret which Young missed and which his French successor,
Jean Francois Champollion, working on the foundation that Young
had laid, was enabled to ferret out.

Young's initial studies of the Rosetta Stone were made in 1814;
his later publication bore date of 1819. Champollion's first
announcement of results came in 1822; his second and more
important one in 1824.  By this time, through study of the
cartouches of other inscriptions, Champollion had made out almost
the complete alphabet, and the "riddle of the Sphinx" was
practically solved.  He proved that the Egyptians had developed a
relatively complete alphabet (mostly neglecting the vowels, as
early Semitic alphabets did also) centuries before the
Phoenicians were heard of in history. What relation this alphabet
bore to the Phoenician we shall have occasion to ask in another
connection; for the moment it suffices to know that those strange
pictures of the Egyptian scroll are really letters.

Even this statement, however, must be in a measure modified.
These pictures are letters and something more.  Some of them are
purely alphabetical in character and some are symbolic in another
way. Some characters represent syllables.  Others stand sometimes
as mere representatives of sounds, and again, in a more extended
sense, as representations of things, such as all hieroglyphics
doubtless were in the beginning.  In a word, this is an alphabet,
but not a perfected alphabet, such as modern nations are
accustomed to; hence the enormous complications and difficulties
it presented to the early investigators.

Champollion did not live to clear up all these mysteries. His
work was taken up and extended by his pupil Rossellini, and in
particular by Dr. Richard Lepsius in Germany, followed by M.
Bernouf, and by Samuel Birch of the British Museum, and more
recently by such well-known Egyptologists as MM.  Maspero and
Mariette and Chabas, in France, Dr. Brugsch, in Germany, and Dr.
E. Wallis Budge, the present head of the Department of Oriental
Antiquities at the British Museum.  But the task of later
investigators has been largely one of exhumation and translation
of records rather than of finding methods.


TREASURES FROM NINEVEH

The most casual wanderer in the British Museum can hardly fail to
notice two pairs of massive sculptures, in the one case winged
bulls, in the other winged lions, both human-headed, which guard
the entrance to the Egyptian hall, close to the Rosetta Stone. 
Each pair of these weird creatures once guarded an entrance to
the palace of a king in the famous city of Nineveh.  As one
stands before them his mind is carried back over some
twenty-seven intervening centuries, to the days when the "Cedar
of Lebanon" was "fair in his greatness" and the scourge of
Israel.

The very Sculptures before us, for example, were perhaps seen by
Jonah when he made that famous voyage to Nineveh some seven or
eight hundred years B.C. A little later the Babylonian and the
Mede revolted against Assyrian tyranny and descended upon the
fair city of Nineveh, and almost literally levelled it to the
ground. But these great sculptures, among other things, escaped
destruction, and at once hidden and preserved by the accumulating
debris of the centuries, they stood there age after age, their
very existence quite forgotten. When Xenophon marched past their
site with the ill-starred expedition of the ten thousand, in the
year 400 B.C., he saw only a mound which seemed to mark the site
of some ancient ruin; but the Greek did not suspect that he
looked upon the site of that city which only two centuries before
had been the mistress of the world.

So ephemeral is fame!  And yet the moral scarcely holds in the
sequel; for we of to-day, in this new, undreamed-of Western
world, behold these mementos of Assyrian greatness fresh from
their twenty-five hundred years of entombment, and with them
records which restore to us the history of that long-forgotten
people in such detail as it was not known to any previous
generation since the fall of Nineveh.  For two thousand five
hundred years no one saw these treasures or knew that they
existed.  One hundred generations of men came and went without
once pronouncing the name of kings Shalmaneser or Asumazirpal or
Asurbanipal.  And to-day, after these centuries of oblivion,
these names are restored to history, and, thanks to the character
of their monuments, are assured a permanency of fame that can
almost defy time itself. It would be nothing strange, but rather
in keeping with their previous mutations of fortune, if the names
of Asurnazirpal and Asurbanipal should be familiar as household
words to future generations that have forgotten the existence of
an Alexander, a Caesar, and a Napoleon.  For when Macaulay's
prospective New Zealander explores the ruins of the British
Museum the records of the ancient Assyrians will presumably still
be there unscathed, to tell their story as they have told it to
our generation, though every manuscript and printed book may have
gone the way of fragile textures.

But the past of the Assyrian sculptures is quite necromantic
enough without conjuring for them a necromantic future. The story
of their restoration is like a brilliant romance of history. 
Prior to the middle of this century the inquiring student could
learn in an hour or so all that was known in fact and in fable of
the renowned city of Nineveh.  He had but to read a few chapters
of the Bible and a few pages of Diodorus to exhaust the important
literature on the subject. If he turned also to the pages of
Herodotus and Xenophon, of Justin and Aelian, these served
chiefly to confirm the suspicion that the Greeks themselves knew
almost nothing more of the history of their famed Oriental
forerunners. The current fables told of a first King Ninus and
his wonderful queen Semiramis; of Sennacherib the conqueror; of
the effeminate Sardanapalus, who neglected the warlike ways of
his ancestors but perished gloriously at the last, with Nineveh
itself, in a self-imposed holocaust.  And that was all. How much
of this was history, how much myth, no man could say; and for all
any one suspected to the contrary, no man could ever know. And
to-day the contemporary records of the city are before us in such
profusion as no other nation of antiquity, save Egypt alone, can
at all rival.  Whole libraries of Assyrian books are at hand that
were written in the seventh century before our era. These, be it
understood, are the original books themselves, not copies.  The
author of that remote time appeals to us directly, hand to eye,
without intermediary transcriber. And there is not a line of any
Hebrew or Greek manuscript of a like age that has been preserved
to us; there is little enough that can match these ancient books
by a thousand years. When one reads Moses or Isaiah, Homer,
Hesiod, or Herodotus, he is but following the
transcription--often unquestionably faulty and probably never in
all parts perfect--of successive copyists of later generations. 
The oldest known copy of the Bible, for example, dates probably
from the fourth century A.D., a thousand years or more after the
last Assyrian records were made and read and buried and
forgotten.

There was at least one king of Assyria--namely, Asurbanipal,
whose palace boasted a library of some ten thousand volumes--a
library, if you please, in which the books were numbered and
shelved systematically, and classified and cared for by an
official librarian.  If you would see some of the documents of
this marvellous library you have but to step past the winged
lions of Asurnazirpal and enter the Assyrian hall just around the
corner from the Rosetta Stone.  Indeed, the great slabs of stone
from which the lions themselves are carved are in a sense books,
inasmuch as there are written records inscribed on their surface.
A glance reveals the strange characters in which these records
are written, graven neatly in straight lines across the stone,
and looking to casual inspection like nothing so much as random
flights of arrow-heads. The resemblance is so striking that this
is sometimes called the arrow-head character, though it is more
generally known as the wedge or cuneiform character. The
inscriptions on the flanks of the lions are, however, only
makeshift books.  But the veritable books are no farther away
than the next room beyond the hall of Asurnazirpal.  They occupy
part of a series of cases placed down the centre of this room.
Perhaps it is not too much to speak of this collection as the
most extraordinary set of documents of all the rare treasures of
the British Museum, for it includes not books alone, but public
and private letters, business announcements, marriage
contracts--in a word, all the species of written records that
enter into the every-day life of an intelligent and cultured
community.

But by what miracle have such documents been preserved through
all these centuries?  A glance makes the secret evident. It is
simply a case of time-defying materials.  Each one of these
Assyrian documents appears to be, and in reality is, nothing more
or less than an inscribed fragment of brick, having much the
color and texture of a weathered terra-cotta tile of modern
manufacture.  These slabs are usually oval or oblong in shape,
and from two or three to six or eight inches in length and an
inch or so in thickness.  Each of them was originally a portion
of brick-clay, on which the scribe indented the flights of
arrowheads with some sharp-cornered instrument, after which the
document was made permanent by baking. They are somewhat fragile,
of course, as all bricks are, and many of them have been more or
less crumbled in the destruction of the palace at Nineveh; but to
the ravages of mere time they are as nearly invulnerable as
almost anything in nature. Hence it is that these records of a
remote civilization have been preserved to us, while the similar
records of such later civilizations as the Grecian have utterly
perished, much as the flint implements of the cave-dweller come
to us unchanged, while the iron implements of a far more recent
age have crumbled away.


HOW THE RECORDS WERE READ

After all, then, granted the choice of materials, there is
nothing so very extraordinary in the mere fact of preservation of
these ancient records. To be sure, it is vastly to the credit of
nineteenth-century enterprise to have searched them out and
brought them back to light. But the real marvel in connection
with them is the fact that nineteenth-century scholarship should
have given us, not the material documents themselves, but a
knowledge of their actual contents. The flight of arrow-heads on
wall or slab or tiny brick have surely a meaning; but how shall
we guess that meaning?  These must be words; but what words?  The
hieroglyphics of the Egyptians were mysterious enough in all
conscience; yet, after all, their symbols have a certain
suggestiveness, whereas there is nothing that seems to promise a
mental leverage in the unbroken succession of these cuneiform
dashes. Yet the Assyrian scholar of to-day can interpret these
strange records almost as readily and as surely as the classical
scholar interprets a Greek manuscript.  And this evidences one of
the greatest triumphs of nineteenth-century scholarship, for
within almost two thousand years no man has lived, prior to our
century, to whom these strange inscriptions would not have been
as meaningless as they are to the most casual stroller who looks
on them with vague wonderment here in the museum to-day. For the
Assyrian language, like the Egyptian, was veritably a dead
language; not, like Greek and Latin, merely passed from practical
every-day use to the closet of the scholar, but utterly and
absolutely forgotten by all the world. Such being the case, it is
nothing less than marvellous that it should have been restored.

It is but fair to add that this restoration probably never would
have been effected, with Assyrian or with Egyptian, had the
language in dying left no cognate successor; for the powers of
modern linguistry, though great, are not actually miraculous. 
But, fortunately, a language once developed is not blotted out in
toto; it merely outlives its usefulness and is gradually
supplanted, its successor retaining many traces of its origin. 
So, just as Latin, for example, has its living representatives in
Italian and the other Romance tongues, the language of Assyria is
represented by cognate Semitic languages. As it chances, however,
these have been of aid rather in the later stages of Assyrian
study than at the very outset; and the first clew to the message
of the cuneiform writing came through a slightly different
channel.

Curiously enough, it was a trilingual inscription that gave the
clew, as in the case of the Rosetta Stone, though with very
striking difference withal. The trilingual inscription now in
question, instead of being a small, portable monument, covers the
surface of a massive bluff at Behistun in western Persia. 
Moreover, all three of its inscriptions are in cuneiform
characters, and all three are in languages that at the beginning
of our century were absolutely unknown.  This inscription itself,
as a striking monument of unknown import, had been seen by
successive generations. Tradition ascribed it, as we learn from
Ctesias, through Diodorus, to the fabled Assyrian queen
Semiramis.  Tradition was quite at fault in this; but it is only
recently that knowledge has availed to set it right. The
inscription, as is now known, was really written about the year
515 B.C., at the instance of Darius I., King of Persia, some of
whose deeds it recounts in the three chief languages of his
widely scattered subjects.

The man who at actual risk of life and limb copied this wonderful
inscription, and through interpreting it became the veritable
"father of Assyriology," was the English general Sir Henry
Rawlinson.  His feat was another British triumph over the same
rivals who had competed for the Rosetta Stone; for some French
explorers had been sent by their government, some years earlier,
expressly to copy this strange record, and had reported that it
was impossible to reach the inscription. But British courage did
not find it so, and in 1835 Rawlinson scaled the dangerous height
and made a paper cast of about half the inscription. Diplomatic
duties called him away from the task for some years, but in 1848
he returned to it and completed the copy of all parts of the
inscription that have escaped the ravages of time. And now the
material was in hand for a new science, which General Rawlinson
himself soon, assisted by a host of others, proceeded to
elaborate.

The key to the value of this unique inscription lies in the fact
that its third language is ancient Persian.  It appears that the
ancient Persians had adopted the cuneiform character from their
western neighbors, the Assyrians, but in so doing had made one of
those essential modifications and improvements which are scarcely
possible to accomplish except in the transition from one race to
another.  Instead of building with the arrow-head a multitude of
syllabic characters, including many homophones, as had been and
continued to be the custom with the Assyrians, the Persians
selected a few of these characters and ascribed to them phonetic
values that were almost purely alphabetic. In a word, while
retaining the wedge as the basal stroke of their script, they
developed an alphabet, making the last wonderful analysis of
phonetic sounds which even to this day has escaped the Chinese,
which the Egyptians had only partially effected, and which the
Phoenicians were accredited by the Greeks with having introduced
to the Western world. In addition to this all-essential step, the
Persians had introduced the minor but highly convenient custom of
separating the words of a sentence from one another by a
particular mark, differing in this regard not only from the
Assyrians and Egyptians, but from the early Greek scribes as
well.

Thanks to these simplifications, the old Persian language had
been practically restored about the beginning of the nineteenth
century, through the efforts of the German Grotefend, and further
advances in it were made just at this time by Renouf, in France,
and by Lassen, in Germany, as well as by Rawlinson himself, who
largely solved the problem of the Persian alphabet independently.
So the Persian portion of the Behistun inscription could be at
least partially deciphered.  This in itself, however, would have
been no very great aid towards the restoration of the languages
of the other portions had it not chanced, fortunately, that the
inscription is sprinkled with proper names.  Now proper names,
generally speaking, are not translated from one language to
another, but transliterated as nearly as the genius of the
language will permit. It was the fact that the Greek word
Ptolemaics was transliterated on the Rosetta Stone that gave the
first clew to the sounds of the Egyptian characters.  Had the
upper part of the Rosetta Stone been preserved, on which,
originally, there were several other names, Young would not have
halted where he did in his decipherment.

But fortune, which had been at once so kind and so tantalizing in
the case of the Rosetta Stone, had dealt more gently with the
Behistun inscriptions; for no fewer than ninety proper names were
preserved in the Persian portion and duplicated, in another
character, in the Assyrian inscription. A study of these gave a
clew to the sounds of the Assyrian characters. The decipherment
of this character, however, even with this aid, proved enormously
difficult, for it was soon evident that here it was no longer a
question of a nearly perfect alphabet of a few characters, but of
a syllabary of several hundred characters, including many
homophones, or different forms for representing the same sound.
But with the Persian translation for a guide on the one hand, and
the Semitic languages, to which family the Assyrian belonged, on
the other, the appalling task was gradually accomplished, the
leading investigators being General Rawlinson, Professor Hincks,
and Mr. Fox-Talbot, in England, Professor Jules Oppert, in Paris,
and Professor Julian Schrader, in Germany, though a host of other
scholars soon entered the field.

This great linguistic feat was accomplished about the middle of
the nineteenth century.  But so great a feat was it that many
scholars of the highest standing, including Joseph Erneste Renan,
in France, and Sir G. Cornewall Lewis, in England, declined at
first to accept the results, contending that the Assyriologists
had merely deceived themselves by creating an arbitrary language.
The matter was put to a test in 1855 at the suggestion of Mr.
Fox-Talbot, when four scholars, one being Mr. Talbot himself and
the others General Rawlinson, Professor Hincks, and Professor
Oppert, laid before the Royal Asiatic Society their independent
interpretations of a hitherto untranslated Assyrian text.  A
committee of the society, including England's greatest historian
of the century, George Grote, broke the seals of the four
translations, and reported that they found them unequivocally in
accord as regards their main purport, and even surprisingly
uniform as regards the phraseology of certain passages--in short,
as closely similar as translations from the obscure texts of any
difficult language ever are. This decision gave the work of the
Assyriologists official status, and the reliability of their
method has never since been in question. Henceforth Assyriology
was an established science.



APPENDIX

REFERENCE-LIST

CHAPTER I. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES

[1] Robert Boyle, Philosophical Works (3 vols.). London, 1738.

CHAPTER II.  THE BEGINNINGS OF MODERN CHEMISTRY 

[1] For a complete account of the controversy called the "Water
Controversy," see The Life of the Hon. Henry Cavendish, by George
Wilson, M.D., F.R.S.E. London, 1850.

[2] Henry Cavendish, in Phil. Trans. for 1784, P. 119.

[3] Lives of the Philosophers of the Time of George III., by
Henry, Lord Brougham, F.R.S., p. 106.  London, 1855.  

[4] Experiments and Observations on Different Kinds of Air, by
Joseph Priestley (3 vols.). Birmingham, 790, vol. II, pp.
103-107.

[5] Lectures on Experimental Philosophy, by Joseph Priestley,
lecture IV., pp. 18, ig. J. Johnson, London, 1794.

[6] Translated from Scheele's Om Brunsten, eller Magnesia, och
dess Egenakaper. Stockholm, 1774, and published as Alembic Club
Reprints, No. 13, 1897, p. 6.

[7] According to some writers this was discovered by Berzelius.

[8] Histoire de la Chimie, par Ferdinand Hoefer. Paris, 1869,
Vol. CL, p. 289.

[9] Elements of Chemistry, by Anton Laurent Lavoisier, translated
by Robert Kerr, p. 8. London and Edinburgh, 1790. 

[10] Ibid., pp. 414-416.

CHAPTER III. CHEMISTRY SINCE THE TIME OF DALTON

[1] Sir Humphry Davy, in Phil. Trans., Vol. VIII.

CHAPTER IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY

[1] Baas, History of Medicine, p. 692.

[2] Based on Thomas H. Huxley's Presidential Address to the
British Association for the Advancement of Science, 1870.

[3] Essays on Digestion, by James Carson. London, 1834, p. 6.

[4] Ibid., p. 7. 

[5] John Hunter, On the Digestion of the Stomach after Death,
first edition, pp. 183-188.

[6] Erasmus Darwin, The Botanic Garden, pp. 448-453. London,
1799.

CHAPTER V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY

[1] Baron de Cuvier's Theory of the Earth. New York, 1818, p.
123.

[2] On the Organs and Mode of Fecundation of Orchidex and
Asclepiadea, by Robert Brown, Esq., in Miscellaneous Botanical
Works. London, 1866, Vol. I., pp.  511-514.

[3] Justin Liebig, Animal Chemistry. London, 1843, p. 17f.

CHAPTER VI. THEORIES OF ORGANIC EVOLUTION

[1] "Essay on the Metamorphoses of Plants," by Goethe, translated
for the present work from Grundriss einer Geschichte der
Naturwissenschaften, by Friederich Dannemann (2 vols.). Leipzig,
1896, Vol. I., p. 194.

[2] The Temple of Nature, or The Origin of Society, by Erasmus
Darwin, edition published in 1807, p. 35.

[3] Baron de Cuvier, Theory of the Earth. New York, 1818, p.74.
(This was the introduction to Cuvier's great work.)

[4] Robert Chambers, Explanations: a sequel to Vestiges of
Creation. London, Churchill, 1845, pp. 148-153.

CHAPTER VII. EIGHTEENTH-CENTURY MEDICINE

[1] Condensed from Dr. Boerhaave's Academical Lectures on the
Theory of Physic. London, 1751, pp. 77, 78. Boerhaave's lectures
were published as Aphorismi de cognoscendis et curandis Morbis,
Leyden, 1709. On this book Van Swieten wrote commentaries filling
five volumes. Another very celebrated work of Boerhaave is his
Institutiones et Experimenta Chemic, Paris, 1724, the germs of
this being given as a lecture on his appointment to the chair of
chemistry in the University of Leyden in 1718.

[2] An Inquiry into the Causes and Effects of the Variola
Vaccine, etc., by Edward Jenner, M.D., F.R.S., etc. London, 1799,
pp. 2-7. He wrote several other papers, most of which were
communications to the Royal Society. His last publication was, On
the Influence of Artificial Eruptions in Certain Diseases
(London, 1822), a subject to which he had given much time and
study.

CHAPTER VIII. NINETEENTH-CENTURY MEDICINE

[1] In the introduction to Corvisart's translation of
Avenbrugger's work. Paris, 1808.

[2] Laennec, Traite d'Auscultation Mediate. Paris, 1819. This was
Laennec's chief work, and was soon translated into several
different languages. Before publishing this he had written also,
Propositions sur la doctrine midicale d'Hippocrate, Paris, 1804,
and Memoires sur les vers visiculaires, in the same year.

[3] Researches, Chemical and Philosophical, chiefly concerning
Nitrous Oxide or Dephlogisticated Nitrous Air and its
Respiration, by Humphry Davy. London, 1800, pp. 479-556.

[4] Ibid.

[5] For accounts of the discovery of anaesthesia, see Report of
the Board of Trustees of the Massachusetts General Hospital,
Boston, 1888. Also, The Ether Controversy: Vindication of the
Hospital Reports of 1848, by N. L Bowditch, Boston, 1848. An
excellent account is given in Littell's Living Age, for March,
1848, written by R. H. Dana, Jr. There are also two Congressional
Reports on the question of the discovery of etherization, one for
1848, the other for 11852.

[6] Simpson made public this discovery of the anaesthetic
properties of chloroform in a paper read before the
Medico-Chirurgical Society of Edinburgh, in March, 1847, about
three months after he had first seen a surgical operation
performed upon a patient to whom ether had been administered.

[7] Louis Pasteur, Studies on Fermentation. London, 1870.

[8] Louis Pasteur, in Comptes Rendus des Sciences de L'Academie
des Sciences, vol. XCII., 1881, pp. 429-435.

CHAPTER IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY

[1] Bell's communications were made to the Royal Society, but his
studies and his discoveries in the field of anatomy of the
nervous system were collected and published, in 1824, as An
Exposition of the Natural System of Nerves of the Human Body:
being a Republication of the Papers delivered to the Royal
Society on the Subject of the Nerves.

[2] Marshall Hall, M.D., F.R.S.L., On the Reflex Functions of the
Medulla Oblongata and the Medulla Spinalis, in Phil. Trans. of
Royal Soc., vol. XXXIII., 1833.





End of Project Gutenberg Etext of A History of Science, V 4, by Williams