[Professor Geddes is Professor of Botany at University
College, Dundee. He has written "Chapters in Modern Botany"
and many botanical articles and papers. Professor Thomson is
Regius Professor of Natural History, Aberdeen University. His
works include "The Study of Animal Life," "Outlines of
Zoölogy," "The Natural History of the Year" and "The Science
of Life." "The Evolution of Sex" was written jointly by both
these authors. The article from which extracts follow was
published in the _Contemporary Review_, 1895: the editor's
permission to reprint is gratefully acknowledged. The Life of
Louis Pasteur by M. Radot, 2 vols., were published by
McClure, Phillips & Co., New York, 1901.]
The course of Pasteur's scientific work is one of remarkably natural and
logical sequence. As the veteran M. Chevreuil long ago said in the
Academy of Sciences, "It is by first examining in their chronological
order the researches of M. Pasteur, and then considering them as a
whole, that we appreciate the rigor of his conclusions, and the
perspicacity of a mind which, strong in the truths which it has already
discovered, sweeps forward to the establishment of what is new." We
shall therefore summarize the record of his greatest achievements.
As was natural in a pupil of Dumas, Balard, and Delafosse, Pasteur's
first important piece of work was chemical and crystallographic, and we
may best understand its spirit by recalling the work of Delafosse's
master in mineralogy, the Abbé Hauy, who is still remembered for that
bold attempt to visualize the ultimate structure of the crystal, to
penetrate the inmost secret of its architecture, which also reappears in
another way in the work of Mendelejeff. Pasteur's puzzle concerned the
tartrates and paratartrates of soda and ammonia. These two salts are
alike in chemical composition, in crystalline form, in specific gravity,
and so on, but they differ in behaviour. Thus, as Biot had shown, a
solution of tartrate deflects the plane of polarized light passed
through it, while a solution of the paratartrate does not. The salts are
the same, yet they behave differently. A note to the Academy from the
famous chemist Mitscherlich emphasized the entire similarity of the two
salts, and this acted as an additional stimulus to Pasteur. He succeeded
in distinguishing the minute facets which even Mitscherlich had missed;
he proved that the paratartrate is a combination of a left-handed and a
right-handed tartrate, and did much else which only the expert chemist
could duly explain. Biot was first doubtful, then delighted; Arago, who
had also busied himself with these matters, moved that Pasteur's paper
be printed in the memoirs of the Academy, and Mitscherlich himself
congratulated the young discoverer who had tripped him up.
Already, then, in this minute and laborious piece of work, we may detect
ultra-microscopic mental vision, and that rigorous accuracy so
characteristic of the man. Yet it is interesting to observe that at this
early stage he was sowing his wild oats of speculation. Impressed by the
strange rotation of the plane of polarization exhibited by these organic
salts, he deduced therefrom an hypothesis of molecular dissymmetry, and
hazarded the view that this was a fundamental distinction between the
organic and the inorganic. For various reasons, neither chemist nor
biologist would nowadays accept this distinction; but it is hard to tell
what Pasteur might have made of this inquiry had not circumstances,
regretted at the time, directed his attention to very different
subjects.
Being thus known in connection with tartrates, Pasteur was one day
consulted, so the story goes, by a German manufacturer of chemicals, who
was puzzled by the fermentation of his commercial tartrate of lime,
which contained some admixture of organic impurities. Pasteur undertook
to look into the matter, and probably deriving some hint from the
previous work of Cagniard Latour, and Schwann who had demonstrated the
yeast-plant which causes alcoholic fermentation, he demonstrated the
micro-organism which fermented the tartrate of lime. He extended this
discovery to other tartrates, and made the neat experiment of showing
how the common blue mould (_Penicillium glaucum_), sown in paratartrate
of ammonia, uses up all the right-handed tartrate and leaves the
left-handed salt alone, its identical chemical composition
notwithstanding. These and similar inquiries led him to tackle the whole
question of fermentation, but his transference to Lille had probably
much to do with this. For, as one of the chief industries of the
district is making alcohol from beet-root and grain, Pasteur's practical
sense led him to devote some of his lectures to fermentation; here, as
always, as his biographer reminds us, wishful to make himself directly
useful to his hearers.
The prevalent theory of fermentation, before Pasteur took the subject in
hand, was that of Willis and Stahl, revised and elaborated by Liebig.
According to this theory, nitrogenous substances in a state of
decomposition upset the molecular equilibrium of fermentable matter with
which they are in contact. What Pasteur did was to show that lactic,
butyric, acetic, and some other fermentations, were due to the vital
activity of micro-organisms. In spite of Liebig's prolonged opposition,
Pasteur carried his point; and although some of his detailed
interpretations have since been revised, it is universally admitted that
he changed the whole complexion of the fermentation problem. It must, of
course, be borne in mind that his theory of the vital nature of many
fermentations does not apply to soluble ferments or enzymes--such as
diastase and pepsin--which are chemical substances, not living
organisms. Part, indeed, of the opposition to Pasteur's views was due to
the fact that this distinction between organized and unorganized
ferments was not at the time clearly drawn. Perhaps, indeed, we are as
yet by no means out of the woods.
In the course of his work on fermentation, Pasteur made an important
theoretical step by distinguishing the micro-organisms which require the
presence of free oxygen, from forms which are able to live apart from
free oxygen, obtaining what they require by splitting up
oxygen-containing compounds in the surrounding medium. These he termed
ærobic and anærobic respectively. Practically, this piece of work
immediately led to what is known as the Orleans process of making
vinegar. Some years later, after he had returned to Paris, he followed
this up by his studies on wine, in the course of which he tracked
various wine-diseases to their sources, and showed how deterioration
might be prevented by raising the wine for a minute to a temperature of
50°C. The wine-tasters of Paris gave their verdict in his favour.
The old notion of spontaneous generation still lingered in some
quarters, and in 1858 Pouchet had given new life to the question by
claiming before the Academy of Sciences that he had succeeded in proving
the origin of microscopic organisms apart from pre-existing germs. But
Pasteur knew more than Pouchet as to the insidious ways of germs: he
showed the weak point of his antagonist's experiments, and gained the
prize, offered in 1860 by the Academy, for "well-contrived experiments
to throw new light upon the question of spontaneous generation." As
every one knows, the victory was with Pasteur, but the idea is an old
and recurrent one, and dies hard. Thus, not many years afterward,
Pasteur and Tyndall had to fight the battle over again with Bastian. The
important result of what seems at first sight an abstract discussion has
been not only an increased knowledge of the distribution and
dissemination of bacteria, but the establishment of the fundamental
conditions and methods of experimental bacteriology....
[Here follows substantially the same narrative as that given by Sir J.
Risdon Bennett on pages 36 to 49 of this volume. It recites how Pasteur
devised preventives for the disease which was destroying the silkworms;
preventives for splenic fever or anthrax.]
Opposition was an ever-recurrent factor in Pasteur's life. He had to
fight for his crystallographic and chemical theories, and for his
fermentation theory; he had to fight against the theory of spontaneous
generation, and for his practice of inoculating as a preventive against
splenic fever; he had to fight for each step. But no part of his work
has met with so much opposition and adverse criticism as that concerning
hydrophobia, though it is easy to exaggerate the importance of the
discussion, in which Pasteur himself took little part. Feeling ran high
in this country; hence, when it was announced that Pasteur--surely best
qualified to speak--was to write the article Hydrophobia in "Chamber's
Encyclopædia," a shower of letters inundated the office; hence the
article in question includes an editorially demanded summary of the
grounds of the opposition by one of ourselves, and to which therefore we
may refer the reader.
While avoiding controversy and partisanship as far as may be, the
question remains, What did Pasteur do in regard to hydrophobia? His
claims are to have proved, first of all, that the disease was
particularly associated with the nervous system. The virus is usually
spread through the saliva, but it is not found in the blood or lymph,
and it has its special seat in the nerves, brain, and spinal cord.
Secondly, he showed that the virus might be attenuated in its virulence.
The spinal cord of a rabbit which has died of rabies, is, when fresh,
powerfully virulent, but when exposed for a couple of weeks to dry air
at a constant temperature of 23°-24°C. it loses its virulence. Thirdly,
he showed that inoculation with the attenuated virus rendered an animal
immune from infection with rabies. To make the animal immune it has
first to be inoculated with infected spinal cord fourteen days old, then
with that of thirteen days, and so on till inoculation with almost
freshly infected spinal cord is possible. In this way the animal becomes
refractory to the infection, and if it be bitten it will not die.
Fourthly, he showed that even if the organism had been bitten, it was
still possible to save it, unless the wounds were near the head--that
is, within close reach of the central nervous system. For in the case of
a superficial wound, say on hand or leg, the virus takes some
considerable time to spread, and during this period of spreading and
incubation it is possible to forestall the virus by inoculation with
that which has been attenuated. In this case there is obvious truth in
the proverb, "He gives twice who gives quickly." And the outcome was,
that while out of a hundred persons bitten, nineteen or twenty will in
ordinary circumstances die, "the mortality among cases treated at the
Pasteur Institute has fallen to less than 1-2 per cent." According to
another set of statistics, a mortality of 40 per cent. has been reduced
to 1.3 per cent.; and of 1673 patients treated by Pasteur's method only
thirteen died.
As to the adverse criticism of Pasteur's inoculation against rabies, it
consists, first and second, of the general argument of the
anti-vaccinationists, and thirdly, of specific objections. To the two
former the school of Pasteur, of course, replies that the value of human
life answers the one, and the results of experience the other; but on
these controversies we cannot enter here. The main specific objections
we take to be three--that as the micro-organism of rabies has not really
been seen, the theory and practice of Pasteur's anti-rabic method lack
that stability which is desirable; that the statistics in favor of the
Pasteur procedure have been insufficiently criticised; that there have
been failures and casualties, sometimes of a tragic nature. In regard to
this last point--that deaths have occurred as the result of the supposed
cure, instead of from the original infection--we may note that the
_possibility_ of such casualties was admitted by the English
Investigation Committee (1887), while, on the other hand, Dr. Armand
Ruffer, who speaks with much authority, denies with all deliberateness
that there is any known case in which death followed as the result of
Pasteur's treatment.
Microscopic verification is, of course, most desirable, and statistics
are proverbially difficult of criticism. But, on the whole, we think it
likely that those who, like ourselves are not medical experts will
incline to believe that Sir James Paget, Dr. Lauder Brunton, Professor
George Fleming, Sir Joseph Lister, Dr. Richard Quain, Sir Henry Roscoe,
and Professor Burdon Sanderson must have had grounds for saying, in the
report which they presented to Parliament in 1887, "It may, hence, be
deemed certain that M. Pasteur has discovered a method of protection
from rabies comparable with that which vaccination affords against
infection from small-pox."
So far a summary of Pasteur's personal life and scientific work, but is
it not possible to make a more general and rational estimate of these?
So much was his life centred in Paris that most people are probably
accustomed to think of him as a townsman; but it is more biologically
accurate to recognize him as a rustic, sprung from a strong, thrifty
stock of mountain peasants. Nor can his rustic early environment of
tanyard and farm, of village and country-side, be overlooked as a factor
in developing that practical sense and economic insight which were so
conspicuous in his life work. The tanner's son becomes the specialist in
fermentation; the country boy is never throughout his life beyond hail
of the poultry-yard and the farm-steading, the wine press and the silk
nursery; brought up in the rural French atmosphere of careful thrift and
minute economies, all centred not round the mechanism or exchange of
town industries, but round the actual maintenance of human and organic
life, he becomes a great life-saver in his generation.
In short, as we might almost diagrammatically sum it up, the shrewd,
minutely careful, yet inquiring rustic, eager to understand and then to
improve what he sees, passes in an ever-widening spiral from his rural
centre upward, from tan-pit to vat and vintage, from manure-heaps,
earthworms, and water-supply to the problems of civic sanitation. The
rustic tragedies of the dead cow and the mad dog excite the explanation
and suggest the prevention, of these disasters; from the poisoning of
rats and mice he passes to suggestive experiments as to the rabbit-pest
of Australia, and so in other cases from beast to man, from village to
state. And on each radius on which he paused he left either a method or
a clew, and set some other inquirer at work. On each radius of work he
has left his disciples; for he founded not only an Institute, but a
living school, or indeed whole schools of workers. We think of him,
then, not only as thinking rustic, but as one of the greatest examples
in science of the Rustic Thinker--a type of thinker too rare in our
mechanical and urban generation, yet for whom the next generation waits.
As to his actual legacy to the world, let us sum it up briefly. There is
the impulse which he gave, after the successful organization of his own
Institute, to the establishment in other countries of similar
laboratories of preventive medicine, and, one may also say, of
experimental evolution. There is his educative work at Strasburg and
Lille, at the Ecole Normale and the Sorbonne, and, above all, in the
smaller yet world-wide circle of his immediate disciples. To general
biology his chief contribution has been the demonstration of the part
which bacteria play, not only in pathological and physiological
processes, but in the wider drama of evolution. To the chemist he has
given a new theory of fermentation; to the physician many a suggestive
lesson in the etiology [inquiry into the causes] of diseases, and a
series of bold experiments in preventive and curative inoculation, of
which Roux's treatment of diphtheria and Professor Fraser's new remedy
for snake-bite are examples at present before the public; to the surgeon
a stable foundation, as Lister acknowledged, for antiseptic treatment;
to the hygienist a multitude of practical suggestions concerning
water-supply and drainage, disinfection and burial. On brewer,
distiller, and wine-maker he has forced the microscope and its results;
and he has shown both agriculturist and stock-breeder how some, at
least, of their many more than ten plagues may be either averted or
alleviated.