the celebrated chemist Dumas, now perpetual secretary of the French
Academy of Sciences. He turned to his friend, colleague, and pupil,
Pasteur, and besought him, with an earnestness which the circumstances
rendered almost personal, to undertake the investigation of the
malady. Pasteur at this time had never seen a silkworm, and he urged
his inexperience in reply to his friend. But Dumas knew too well the
qualities needed for such an enquiry to accept Pasteur's reason for
declining it. 'Je mets,' said he, 'un prix extréme à voir votre
attention fixée sur la question qui intéresse mon pauvre pays; la
misére surpasse tout ce que vous pouvez imaginer.' Pamphlets about the
plague had been showered upon the public, the monotony of waste paper
being broken, at rare intervals, by a more or less useful publication.
'The Pharmacopoeia of the Silkworm,' wrote M. Cornalia in 1860, 'is
now as complicated as that of man. Gases, liquids, and solids have
been laid under contribution. From chlorine to sulphurous acid, from
nitric acid to rum, from sugar to sulphate of quinine,--all has been
invoked in behalf of this unhappy insect.' The helpless cultivators,
moreover, welcomed with ready trustfulness every new remedy, if only
pressed upon them with sufficient hardihood. It seemed impossible to
diminish their blind confidence in their blind guides. In 1863 the
French Minister of Agriculture signed an agreement to pay 500,000
francs for the use of a remedy, which its promoter declared to be
infallible. It was tried in twelve different departments of France,
and found perfectly useless. In no single instance was it successful.
It was under these circumstances that M. Pasteur, yielding to the
entreaties of his friend, betook himself to Alais in the beginning of
June, 1865. As regards silk husbandry, this was the most important
department in France, and it was the most sorely smitten by the
plague.
The silkworm had been previously attacked by muscardine, a disease
proved by Bassi to be caused by a vegetable parasite. This malady was
propagated annually by the parasitic spores. Wafted by winds they
often sowed the disease in places far removed from the centre of
infection. Muscardine is now said to be very rare, a deadlier malady
having taken its place. This new disease is characterised by the
black spots which cover the silkworms; hence the name _pébrine_, first
applied to the plague by M. de Quatrefages, and adopted by Pasteur.
_pébrine_ declares itself in the stunted and unequal growth of the
worms, in the languor of their movements, in their fastidiousness as
regards food, and in their premature death. The course of discovery
as regards the epidemic is this: In 1849 Guérin Méneville noticed in
the blood of silkworms vibratory corpuscles, which he supposed from
their motions to be endowed with independent life. Filippi, however,
showed that the motion of the corpuscles was the well-known Brownian
motion; but he committed the error of supposing the corpuscles to be
normal to the life of the insect. Possessing the power of indefinite
self-multiplication, they are really the cause of its mortality--the
form and substance of its disease. This was well described by
Cornalia; while Lebert and Frey subsequently found the corpuscles not
only in the blood, but in all the tissues of the insect. Osimo, in
1857, discovered them in the eggs; and on this observation Vittadiani
founded, in 1859, a practical method of distinguishing healthy from
diseased eggs. The test often proved fallacious, and it was never
extensively applied.
These living corpuscles take possession of the intestinal canal, and
spread thence throughout the body of the worm. They fill the silk
cavities, the stricken insect often going automatically through the
motions of spinning, without any material to work upon. Its organs,
instead of being filled with the clear viscous liquid of the silk, are
packed to distension by the corpuscles. On this feature of the plague
Pasteur fixed his entire attention. The cycle of the silkworm's life
is briefly this: From the fertile egg comes the little worm, which
grows, and casts its skin. This process of moulting is repeated two
or three times at intervals during the life of the insect. After the
last moulting the worm climbs the brambles placed to receive it, and
spins among them its cocoon. It passes thus into a chrysalis; the
chrysalis becomes a moth, and the moth, when liberated, lays the eggs
which form the starting-point of a new cycle. Now Pasteur proved that
the plague-corpuscles might be incipient in the egg, and escape
detection; they might also be germinal in the worm, and still baffle
the microscope. But as the worm grows, the corpuscles grow also,
becoming larger and more defined. In the aged chrysalis they are more
pronounced than in the worm; while in the moth, if either the egg or
the worm from which it comes should have been at all stricken, the
corpuscles infallibly appear, offering no difficulty of detection.
This was the first great point made out in 1865 by Pasteur. The
Italian naturalists, as aforesaid, recommended the examination of the
eggs before risking their incubation. Pasteur showed that both eggs
and worms might be smitten, and still pass muster, the culture of such
eggs or such worms being sure to entail disaster. He made the moth
his starting-point in seeking to regenerate the race.
Pasteur made his first communication on this subject to the Academy of
Sciences in September, 1865. It raised a cloud of criticism. Here,
forsooth, was a chemist rashly quitting his proper _métier_ and
presuming to lay down the law for the physician and biologist on a
subject which was eminently theirs. 'On trouva étrange que je fusse
si peu au courant de la question; on m'opposa des travaux qui avaient
paru depuis longtemps en Italie, dont les résultats montraient
l'inutilité de mes efforts, et l'impossibilité d'arriver à un résultat
pratique dans la direction que je m'étais engagé. Que mon ignorance
fut grande au sujet des recherches sans nombre qui avaient paru depuis
quinze années.' Pasteur heard the buzz, but he continued his work. In
choosing the eggs intended for incubation, the cultivators selected
those produced in the successful 'educations' of the year. But they
could not understand the frequent and often disastrous failures of
their selected eggs; for they did not know, and nobody prior to
Pasteur was competent to tell them, that the finest cocoons may
envelope doomed corpusculous moths. It was not, however, easy to make
the cultivators accept new guidance. To strike their imagination, and
if possible determine their practice, Pasteur hit upon the expedient
of prophecy. In 1866 he inspected, at St. Hippolyte-du-Fort, fourteen
different parcels of eggs intended for incubation. Having examined a
sufficient number of the moths which produced these eggs, he wrote out
the prediction of what would occur in 1867, and placed the prophecy as
a sealed letter in the hands of the Mayor of St. Hippolyte.
In 1867 the cultivators communicated to the mayor their results. The
letter of Pasteur was then opened and read, and it was found that in
twelve out of fourteen cases there was absolute conformity between his
prediction and the observed facts. Many of the groups had perished
totally; the others had perished almost totally; and this was the
prediction of Pasteur. In two out of the fourteen cases, instead of
the prophesied destruction, half an average crop was obtained. Now,
the parcels of eggs here referred to were considered healthy by their
owners. They had been hatched and tended in the firm hope that the
labour expended on them would prove remunerative. The application of
the moth-test for a few minutes in 1866, would have saved the labour
and averted the disappointment. Two additional parcels of eggs were
at the same time submitted to Pasteur. He pronounced them healthy;
and his words were verified by the production of an excellent crop.
Other cases of prophecy still more remarkable, because more
circumstantial, are recorded in Pasteur's work.
Pasteur subjected the development of the corpuscles to a searching
investigation, and followed out with admirable skill and completeness
the various modes by which the plague was propagated. From moths
perfectly free from corpuscles he obtained healthy worms, and
selecting 10, 20, 30, 50, as the case might be, he introduced into the
worms the corpusculous matter. It was first permitted to accompany the
food. Let its take a single example out of many. Rubbing up a small
corpusculous worm in water, he smeared the mixture over the
mulberry-leaves. Assuring himself that the leaves had been eaten, he
watched the consequences from day to day. Side by side with the
infected worms he reared their fellows, keeping them as much as
possible out of the way of infection. These constituted his 'lot
témoin,'--his standard of comparison. On April 16, 1868, he thus
infected thirty worms. Up to the 23rd they remained quite well. On the
25th they seemed well, but on that day corpuscles were found in the
intestines of two of them. On the 27th, or eleven days after the
infected repast, two fresh worms were examined, and not only was the
intestinal canal found in each case invaded, but the silk organ itself
was charged with corpuscles. On the 28th the twenty-six remaining
worms were covered by the black spots of _pébrine_. On the 30th the
difference of size between the infected and non-infected worms was
very striking, the sick worms being not more than two-thirds of the
bulk of the healthy ones. On May 2 a worm which had just finished its
fourth moulting was examined. Its whole body was so filled with the
parasite as to excite astonishment that it could live.
The disease advanced, the worms died and were examined, and on May 11
only six out of the thirty remained. They were the strongest of the
lot, but on being searched they also were found charged with
corpuscles. Not one of the thirty worms had escaped; a single meal had
poisoned them all. The standard lot, on the contrary, spun their fine
cocoons, two only of their moths being proved to contain any trace of
the parasite, which had doubtless been introduced during the rearing
of the worms.
As his acquaintance with the subject increased, Pasteur's desire for
precision augmented, and he finally counted the growing number of
corpuscles seen in the field of his microscope from day to day. After
a contagious repast the number of worms containing the parasite
gradually augmented until finally it became cent. per cent. The number
of corpuscles would at the same time rise from 0 to 1, to 10, to 100,
and sometimes even to 1,000 or 1,500 in the field of his microscope.
He then varied the mode of infection. He inoculated healthy worms with
the corpusculous matter, and watched the consequent growth of the
disease. He proved that the worms inoculate each other by the
infliction of visible wounds with their claws. In various cases he
washed the claws, and found corpuscles in the water. He demonstrated
the spread of infection by the simple association of healthy and
diseased worms. By their claws and their dejections, the diseased
worms spread infection. It was no hypothetical infected medium--no
problematical pythogenic gas--that killed the worms, but a definite
organism. The question of infection at a distance was also examined,
and its existence demonstrated. As might be expected from Pasteur's
antecedents, the investigation was exhaustive, the skill and beauty of
his manipulation finding fitting correlatives in the strength and
clearness of his thought.
The following quotation from Pasteur's work clearly shows the relation
in which his researches stand to the important question on which he
was engaged:
*****
Place (he says) the most skilful educator, even the most expert
microscopist, in presence of large educations which present the
symptoms described in our experiments; his judgment will necessarily
be erroneous if he confines himself to the knowledge which preceded my
researches. The worms will not present to him the slightest spot of
_pébrine_; the microscope will not reveal the existence of corpuscles;
the mortality of the worms will be null or insignificant; and the
cocoons leave nothing to be desired. Our observer would, therefore,
conclude without hesitation that the eggs produced will be good for
incubation. The truth is, on the contrary, that all the worms of
these fine crops have been poisoned; that from the beginning they
carried in them the germ of the malady; ready to multiply itself
beyond measure in the chrysalides and the moths, thence to pass into
the eggs and smite with sterility the next generation. And what is
the first cause of the evil concealed under so deceitful an exterior?
In our experiments we can, so to speak, touch it with our fingers. It
is entirely the effect of a single corpusculous repast; an effect more
or less prompt according to the epoch of life of the worm that has
eaten the poisoned food.
*****
Pasteur describes in detail his method of securing healthy eggs. It
is nothing less than a mode of restoring to France her ancient silk
husbandry. The justification of his work is to be found in the
reports which reached him of the application and the unparalleled
success of his method, while editing his researches for final
publication. In both France and Italy his method has been pursued
with the most surprising results. But it was an up-hill fight which
led to this triumph.
'Ever,' he says, 'since the commencement of these researches, I have
been exposed to the most obstinate and unjust contradictions; but I
have made it a duty to leave no trace of these conflicts in this
book.' And in reference to parasitic diseases, generally, he uses the
following weighty words: 'Il est au pouvoir de l'homme de faire
disparaitre de la surface du globe les maladies parasitaires, si,
comme c'est ma conviction, la doctrine des générations spontanées est
une chimère.'
Pasteur dwells upon the ease with which an island like Corsica might
be absolutely isolated from the silkworm epidemic. And with regard to
other epidemics, Mr. Simon describes an extraordinary case of insular
exemption, for the ten years extending from 1851 to 1860. Of the 627
registration districts of England, one only had an entire escape from
diseases which, in whole or in part, were prevalent in all the others:
'In all the ten years it had not a single death by measles, nor a
single death by small-pox, nor a single death by scarlet-fever. And
why? Not because of its general sanitary merits, for it had an
average amounts of other evidence of unhealthiness. Doubtless, the
reason of its escape was that it was insular. It was the district of
the Scilly Isles; to which it was most improbable that any febrile
contagion should come from without. And its escape is an
approximative proof that, at least for those ten years, no _contagium_
of measles, nor any _contagium_ of scarlet-fever, nor any _contagium_ of
smallpox had arisen spontaneously within its limits.' It may be added
that there were only seven districts in England in which no death from
diphtheria occurred, and that, of those seven districts, the district
of the Scilly Isles was one.
A second parasitic disease of silkworms, called in France _la
Flacherie_, co-existent with _pébrine_, but quite distinct from it, has
also been investigated by Pasteur. Enough, however, has been said to
send the reader interested in these questions to the original volumes
for further information. To one important practical point M. Pasteur,
in a letter to myself, directs attention:
*****
Permettez-moi de terminer ces quelques lignes que je dois dicter,
vaincu que je suis par la maladie, en vous faisant observer que vous
rendriez service aux Colonies de la Grande-Bretagne en répandant la
connaissance de ce livre, et des principes que j'établis touchant la
maladie des vers à soie. Beaucoup de ces colonies pourraient cultiver
le mûrier avec succés, et, en jetant les yeux sur mon ouvrage, vous
vous convaincrez aisement qu'il est facile aujourd'hui, nonseulement
d'éloigner la maladie régnante, mais en outre de donner aux récoltes
de la soie une prospérité qu'elles n'ont jamais eue.
Origin and Propagation of Contagious Matter.
Prior to Pasteur, the most diverse and contradictory opinions were
entertained as to the contagious character of _pébrine_; some stoutly
affirmed it, others as stoutly denied it. But on one point all were
agreed. I They believed in the existence of a deleterious medium,
rendered epidemic by some occult and mysterious influence, to which
was attributed the cause of the disease.' Those acquainted with our
medical literature will not fail to observe an instructive analogy
here. We have on the one side accomplished writers ascribing epidemic
diseases to 'deleterious media' which arise spontaneously in crowded
hospitals and ill-smelling drains. According to them, the _contagia_ of
epidemic disease are formed _de novo_ in a putrescent atmosphere. On
the other side we have writers, clear, vigorous, with well-defined
ideas and methods of research, contending that the matter which
produces epidemic disease comes always from a parent stock. It
behaves as germinal matter, and they do not hesitate to regard it as
such. They no more believe in the spontaneous generation of such
diseases, than they do in the spontaneous generation of mice. Pasteur,
for example, found that _pébrine_ had been known for an indefinite time
as a disease among silkworms. The development of it which he combated
was merely the expansion of an already existing power--the bursting
into open conflagration of a previously smouldering fire. There is
nothing surprising in this. For though epidemic disease requires a
special _contagium_ to produce it, surrounding conditions must have a
potent influence on its development. Common seeds may be duly sown,
but the conditions of temperature and moisture may be such as to
restrict, or altogether prevent, the subsequent growth. Looked at,
therefore, from the point of view of the germ theory, the exceptional
energy which epidemic disease from time to time exhibits, is in
harmony with the method of Nature. We sometimes hear diphtheria
spoken of as if it were a new disease of the last twenty years; but
Mr. Simon tells me that about three centuries ago tremendous epidemics
of it began to rage in Spain (where it was named _Garrotillo_), and soon
afterwards in Italy; and that since that time the disease has been
well known to all successive generations of doctors. In or about
1758, for instance, Dr. Starr, of Liskeard, in a communication to the
Royal Society, particularly described the disease, with all the
characters which have recently again become familiar, but under the
name of _morbus strangulatorius_, as then severely epidemic in Cornwall.
This fact is the more interesting, as diphtheria, in its more modern
reappearance, again showed predilection for that remote county. Many
also believe that the Black Death, of five centuries ago, has
disappeared as mysteriously as it came; but Mr. Simon finds that it is
believed to be prevalent at this hour in some of the north-western
parts of India.
Let me here state an item of my own experience. When I was at the Bel
Alp in 1869, the English chaplain received letters informing him of
the breaking out of scarlet-fever among his children. He lived, if I
remember rightly, on the healthful eminence of Dartmoor, and it was
difficult to imagine how scarlet-fever could have been wafted to the
place. A drain ran close to his house, and on it his suspicions were
manifestly fixed. Some of our medical writers would fortify him in
this notion, and thus deflect him from the truth, while those of
another, and, in my opinion, a wiser school, would deny to a drain,
however foul, the power of generating _de novo_ a specific disease.
After close enquiry he recollected that a hobby-horse had been used
both by his boy and another, who, a short time previously, had passed
through scarlet-fever.
Drains and cesspools, indeed, are by no means in such evil odour as
they used to be. A fetid Thames and a low death-rate occur from time
to time together in London. For, if the special matter or germs of
epidemic disorder be not present, a corrupt atmosphere, however
obnoxious otherwise, will not produce the disorder. But, if the germs
be present, defective drains and cesspools become the potent
distributors of disease and death. Corrupted air may promote an
epidemic, but cannot produce it. On the other hand, through the
transport of the special germ or virus, disease may develop itself in
regions where the drainage is good and the atmosphere pure.
If you see a new thistle growing in your field, you feel sure that its
seed has been wafted thither. Just as sure does it seem that the
contagious matter of epidemic disease has been transplanted to the
place where it newly appears. With a clearness and conclusiveness s
not to be surpassed, Dr. William Budd has traced such diseases from
place to place; showing how they plant themselves, at distinct foci,
among populations subjected to the same atmospheric influences, just
as grains of corn might be carried in the pocket and sown. Hildebrand,
to whose remarkable work, 'Du Typhus contagieux,' Dr. de Mussy has
directed my attention, gives the following striking case, both of the
durability and the transport of the virus of scarlatina: 'Un habit
noir que j'avais en visitant une malade attaquée de scarlatina, et que
je portai de Vienne en Podolie, sans l'avoir mis depuis plus d'un an
et demi, me communiqua, dès que je fus arrivé, cette maladie
contagieuse, que je répandis ensuite dans cette province, où elle
était jusqu'alors presque inconnue.' Some years ago Dr. de Mussy
himself was summoned to a country house in Surrey, to see a young lady
who was suffering from a dropsy, evidently the consequence of
scarlatina. The original disease, being of a very mild character, had
been quite overlooked; but circumstances were recorded which could
leave no doubt upon the mind as to the nature and cause of the
complaint. But then the question arose, How did the young lady catch
the scarlatina? She had come there on a visit two months previously,
and it was only after she had been a month in the house that she was
taken ill. The housekeeper at length cleared up the mystery. The
young lady, on her arrival, had expressed a wish to occupy a room in
an isolated tower. Her desire was granted; and in that room, six
months previously, a visitor had been confined with an attack of
scarlatina. The room had been swept and whitewashed, but the carpets
had been permitted to remain.
Thousands of cases could probably be cited in which the disease has
shown itself in this mysterious way, but where a strict examination
has revealed its true parentage and extraction. Is it, then,
philosophical to take refuge in the fortuitous concourse of atoms as a
cause of specific disease, merely because in special cases the
parentage may be indistinct? Those best acquainted with atomic
nature, and who are most ready to admit, as regards even higher things
than this, the potentialities of matter, will be the last to accept
these rash hypotheses.
The Germ Theory applied to Surgery.
Not only medical but still more especially surgical science is now
seeking light and guidance from this germ theory. Upon it the
antiseptic system of Professor Lister of Edinburgh is founded. As
already stated, the germ theory of putrefaction was started by
Schwann; but the illustrations of this theory adduced by Professor
Lister are of such public moment as not only to justify, but to render
imperative, their introduction here.