record of the commencement of life, and therefore I am devoid of any
means of forming a definite conclusion as to the conditions of its
appearance. Belief, in the scientific sense of the word, is a serious
matter, and needs strong foundations. To say, therefore, in the admitted
absence of evidence, that I have any belief as to the mode in which the
existing forms of life have originated, would be using words in a wrong
sense. But expectation is permissible where belief is not; and if it were
given me to look beyond the abyss of geologically recorded time to the
still more remote period when the earth was passing through physical and
chemical conditions, which it can no more see again than a man can recall
his infancy, I should expect to be a witness of the evolution of living
protoplasm from not living matter. I should expect to see it appear under
forms of great simplicity, endowed, like existing fungi, with the power
of determining the formation of new protoplasm from such matters as
ammonium carbonates, oxalates and tartrates, alkaline and earthy
phosphates, and water, without the aid of light. That is the expectation
to which analogical reasoning leads me; but I beg you once more to
recollect that I have no right to call my opinion anything but an act of
philosophical faith.
So much for the history of the progress of Redi's great doctrine of
Biogenesis, which appears to me, with the limitations I have expressed,
to be victorious along the whole line at the present day.
As regards the second problem offered to us by Redi, whether Xenogenesis
obtains, side by side with Homogenesis,--whether, that is, there exist
not only the ordinary living things, giving rise to offspring which run
through the same cycle as themselves, but also others, producing
offspring which are of a totally different character from themselves,--
the researches of two centuries have led to a different result. That the
grubs found in galls are no product of the plants on which the galls
grow, but are the result of the introduction of the eggs of insects into
the substance of these plants, was made out by Vallisnieri, Réaumur, and
others, before the end of the first half of the eighteenth century. The
tapeworms, bladderworms, and flukes continued to be a stronghold of the
advocates of Xenogenesis for a much longer period. Indeed, it is only
within the last thirty years that the splendid patience of Von Siebold,
Van Beneden, Leuckart, Küchenmeister, and other helminthologists, has
succeeded in tracing every such parasite, often through the strangest
wanderings and metamorphoses, to an egg derived from a parent, actually
or potentially like itself; and the tendency of inquiries elsewhere has
all been in the same direction. A plant may throw off bulbs, but these,
sooner or later, give rise to seeds or spores, which develop into the
original form. A polype may give rise to Medusae, or a pluteus to an
Echinoderm, but the Medusa and the Echinoderm give rise to eggs which
produce polypes or glutei, and they are therefore only stages in the
cycle of life of the species.
But if we turn to pathology, it offers us some remarkable approximations
to true Xenogenesis.
As I have already mentioned, it has been known since the time of
Vallisnieri and of Réaumur, that galls in plants, and tumours in cattle,
are caused by insects, which lay their eggs in those parts of the animal
or vegetable frame of which these morbid structures are outgrowths.
Again, it is a matter of familiar experience to everybody that mere
pressure on the skin will give rise to a corn. Now the gall, the tumour,
and the corn are parts of the living body, which have become, to a
certain degree, independent and distinct organisms. Under the influence
of certain external conditions, elements of the body, which should have
developed in due subordination to its general plan, set up for themselves
and apply the nourishment which they receive to their own purposes.
From such innocent productions as corns and warts, there are all
gradations to the serious tumours which, by their mere size and the
mechanical obstruction they cause, destroy the organism out of which they
are developed; while, finally, in those terrible structures known as
cancers, the abnormal growth has acquired powers of reproduction and
multiplication, and is only morphologically distinguishable from the
parasitic worm, the life of which is neither more nor less closely bound
up with that of the infested organism.
If there were a kind of diseased structure, the histological elements of
which were capable of maintaining a separate and independent existence
out of the body, it seems to me that the shadowy boundary between morbid
growth and Xenogenesis would be effaced. And I am inclined to think that
the progress of discovery has almost brought us to this point already. I
have been favoured by Mr. Simon with an early copy of the last published
of the valuable "Reports on the Public Health," which, in his capacity of
their medical officer, he annually presents to the Lords of the Privy
Council. The appendix to this report contains an introductory essay "On
the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is
one of the clearest, most comprehensive, and well-reasoned discussions of
a great question which has come under my notice for a long time. I refer
you to it for details and for the authorities for the statements I am
about to make.
You are familiar with what happens in vaccination. A minute cut is made
in the skin, and an infinitesimal quantity of vaccine matter is inserted
into the wound. Within a certain time a vesicle appears in the place of
the wound, and the fluid which distends this vesicle is vaccine matter,
in quantity a hundred or a thousandfold that which was originally
inserted. Now what has taken place in the course of this operation? Has
the vaccine matter, by its irritative property, produced a mere blister,
the fluid of which has the same irritative property? Or does the vaccine
matter contain living particles, which have grown and multiplied where
they have been planted? The observations of M. Chauveau, extended and
confirmed by Dr. Sanderson himself, appear to leave no doubt upon this
head. Experiments, similar in principle to those of Helmholtz on
fermentation and putrefaction, have proved that the active element in the
vaccine lymph is non-diffusible, and consists of minute particles not
exceeding 1/20000th of an inch in diameter, which are made visible in the
lymph by the microscope. Similar experiments have proved that two of the
most destructive of epizootic diseases, sheep-pox and glanders, are also
dependent for their existence and their propagation upon extremely small
living solid particles, to which the title of _microzymes_ is applied. An
animal suffering under either of these terrible diseases is a source of
infection and contagion to others, for precisely the same reason as a tub
of fermenting beer is capable of propagating its fermentation by
"infection," or "contagion," to fresh wort. In both cases it is the solid
living particles which are efficient; the liquid in which they float, and
at the expense of which they live, being altogether passive.
Now arises the question, are these microzymes the results of
_Homogenesis_, or of _Xenogenesis?_ are they capable, like the
_Toruloe_ of yeast, of arising only by the development of pre-existing
germs? or may they be, like the constituents of a nut-gall, the results
of a modification and individualisation of the tissues of the body in
which they are found, resulting from the operation of certain conditions?
Are they parasites in the zoological sense, or are they merely what
Virchow has called "heterologous growths"? It is obvious that this
question has the most profound importance, whether we look at it from a
practical or from a theoretical point of view. A parasite may be stamped
out by destroying its germs, but a pathological product can only be
annihilated by removing the conditions which give rise to it.
It appears to me that this great problem will have to be solved for each
zymotic disease separately, for analogy cuts two ways. I have dwelt upon
the analogy of pathological modification, which is in favour of the
xenogenetic origin of microzymes; but I must now speak of the equally
strong analogies in favour of the origin of such pestiferous particles by
the ordinary process of the generation of like from like.
It is, at present, a well-established fact that certain diseases, both of
plants and of animals, which have all the characters of contagious and
infectious epidemics, are caused by minute organisms. The smut of wheat
is a well-known instance of such a disease, and it cannot be doubted that
the grape-disease and the potato-disease fall under the same category.
Among animals, insects are wonderfully liable to the ravages of
contagious and infectious diseases caused by microscopic _Fungi_.
In autumn, it is not uncommon to see flies motionless upon a window-pane,
with a sort of magic circle, in white, drawn round them. On microscopic
examination, the magic circle is found to consist of innumerable spores,
which have been thrown off in all directions by a minute fungus called
_Empusa muscoe_, the spore-forming filaments of which stand out like a
pile of velvet from the body of the fly. These spore-forming filaments
are connected with others which fill the interior of the fly's body like
so much fine wool, having eaten away and destroyed the creature's
viscera. This is the full-grown condition of the _Empusa_. If traced back
to its earliest stages, in flies which are still active, and to all
appearance healthy, it is found to exist in the form of minute corpuscles
which float in the blood of the fly. These multiply and lengthen into
filaments, at the expense of the fly's substance; and when they have at
last killed the patient, they grow out of its body and give off spores.
Healthy flies shut up with diseased ones catch this mortal disease, and
perish like the others. A most competent observer, M. Cohn, who studied
the development of the _Empusa_ very carefully, was utterly unable to
discover in what manner the smallest germs of the _Empusa_ got into the
fly. The spores could not be made to give rise to such germs by
cultivation; nor were such germs discoverable in the air, or in the food
of the fly. It looked exceedingly like a case of Abiogenesis, or, at any
rate, of Xenogenesis; and it is only quite recently that the real course
of events has been made out. It has been ascertained, that when one of
the spores falls upon the body of a fly, it begins to germinate, and
sends out a process which bores its way through the fly's skin; this,
having reached the interior cavities of its body, gives off the minute
floating corpuscles which are the earliest stage of the _Empusa_. The
disease is "contagious," because a healthy fly coming in contact with a
diseased one, from which the spore-bearing filaments protrude, is pretty
sure to carry off a spore or two. It is "infectious" because the spores
become scattered about all sorts of matter in the neighbourhood of the
slain flies.
The silkworm has long been known to be subject to a very fatal and
infectious disease called the _Muscardine_. Audouin transmitted it by
inoculation. This disease is entirely due to the development of a fungus,
_Botrytis Bassiana_, in the body of the caterpillar; and its
contagiousness and infectiousness are accounted for in the same way as
those of the fly-disease. But, of late years, a still more serious
epizootic has appeared among the silkworms; and I may mention a few facts
which will give you some conception of the gravity of the injury which it
has inflicted on France alone.
The production of silk has been for centuries an important branch of
industry in Southern France, and in the year 1853 it had attained such a
magnitude that the annual produce of the French sericulture was estimated
to amount to a tenth of that of the whole world, and represented a money-
value of 117,000,000 francs, or nearly five millions sterling. What may
be the sum which would represent the money-value of all the industries
connected with the working up of the raw silk thus produced, is more than
I can pretend to estimate. Suffice it to say, that the city of Lyons is
built upon French silk as much as Manchester was upon American cotton
before the civil war.
Silkworms are liable to many diseases; and, even before 1853, a peculiar
epizootic, frequently accompanied by the appearance of dark spots upon
the skin (whence the name of "Pébrine" which it has received), had been
noted for its mortality. But in the years following 1853 this malady
broke out with such extreme violence, that, in 1858, the silk-crop was
reduced to a third of the amount which it had reached in 1853; and, up
till within the last year or two, it has never attained half the yield of
1853. This means not only that the great number of people engaged in silk
growing are some thirty millions sterling poorer than they might have
been; it means not only that high prices have had to be paid for imported
silkworm eggs, and that, after investing his money in them, in paying for
mulberry-leaves and for attendance, the cultivator has constantly seen
his silkworms perish and himself plunged in ruin; but it means that the
looms of Lyons have lacked employment, and that, for years, enforced
idleness and misery have been the portion of a vast population which, in
former days, was industrious and well-to-do.
In 1858 the gravity of the situation caused the French Academy of
Sciences to appoint Commissioners, of whom a distinguished naturalist, M.
de Quatrefages, was one, to inquire into the nature of this disease, and,
if possible, to devise some means of staying the plague. In reading the
Report[11] made by M. de Quatrefages in 1859, it is exceedingly
interesting to observe that his elaborate study of the Pébrine forced the
conviction upon his mind that, in its mode of occurrence and propagation,
the disease of the silkworm is, in every respect, comparable to the
cholera among mankind. But it differs from the cholera, and so far is a
more formidable malady, in being hereditary, and in being, under some
circumstances, contagious as well as infectious.
[Footnote 11: _Études sur les Maladies actuelles des Vers à Soie_, p.
53.]
The Italian naturalist, Filippi, discovered in the blood of the silkworms
affected by this strange disorder a multitude of cylindrical corpuscles,
each about 1/6000th of an inch long. These have been carefully studied by
Lebert, and named by him _Panhistophyton_; for the reason that in
subjects in which the disease is strongly developed, the corpuscles swarm
in every tissue and organ of the body, and even pass into the undeveloped
eggs of the female moth. But are these corpuscles causes, or mere
concomitants, of the disease? Some naturalists took one view and some
another; and it was not until the French Government, alarmed by the
continued ravages of the malady, and the inefficiency of the remedies
which had been suggested, despatched M. Pasteur to study it, that the
question received its final settlement; at a great sacrifice, not only of
the time and peace of mind of that eminent philosopher, but, I regret to
have to add, of his health.
But the sacrifice has not been in vain. It is now certain that this
devastating, cholera-like, Pébrine, is the effect of the growth and
multiplication of the _Panhistophyton_ in the silkworm. It is contagious
and infectious, because the corpuscles of the _Panhistophyton_ pass away
from the bodies of the diseased caterpillars, directly or indirectly, to
the alimentary canal of healthy silkworms in their neighbourhood; it is
hereditary because the corpuscles enter into the eggs while they are
being formed, and consequently are carried within them when they are
laid; and for this reason, also, it presents the very singular
peculiarity of being inherited only on the mother's side. There is not a
single one of all the apparently capricious and unaccountable phenomena
presented by the Pébrine, but has received its explanation from the fact
that the disease is the result of the presence of the microscopic
organism, _Panhistophyton_.
Such being the facts with respect to the Pébrine, what are the
indications as to the method of preventing it? It is obvious that this
depends upon the way in which the _Panhistophyton_ is generated. If it
may be generated by Abiogenesis, or by Xenogenesis, within the silkworm
or its moth, the extirpation of the disease must depend upon the
prevention of the occurrence of the conditions under which this
generation takes place. But if, on the other hand, the _Panhistophyton_
is an independent organism, which is no more generated by the silkworm
than the mistletoe is generated by the apple-tree or the oak on which it
grows, though it may need the silkworm for its development in the same
way as the mistletoe needs the tree, then the indications are totally
different. The sole thing to be done is to get rid of and keep away the
germs of the _Panhistophyton_. As might be imagined, from the course of
his previous investigations, M. Pasteur was led to believe that the
latter was the right theory; and, guided by that theory, he has devised a
method of extirpating the disease, which has proved to be completely
successful wherever it has been properly carried out.
There can be no reason, then, for doubting that, among insects,
contagious and infectious diseases, of great malignity, are caused by
minute organisms which are produced from pre-existing germs, or by
homogenesis; and there is no reason, that I know of, for believing that
what happens in insects may not take place in the highest animals.
Indeed, there is already strong evidence that some diseases of an
extremely malignant and fatal character to which man is subject, are as
much the work of minute organisms as is the Pébrine. I refer for this
evidence to the very striking facts adduced by Professor Lister in his
various well-known publications on the antiseptic method of treatment. It
appears to me impossible to rise from the perusal of those publications
without a strong conviction that the lamentable mortality which so
frequently dogs the footsteps of the most skilful operator, and those
deadly consequences of wounds and injuries which seem to haunt the very
walls of great hospitals, and are, even now, destroying more men than die
of bullet or bayonet, are due to the importation of minute organisms into
wounds, and their increase and multiplication; and that the surgeon who
saves most lives will be he who best works out the practical consequences
of the hypothesis of Redi.
I commenced this Address by asking you to follow me in an attempt to
trace the path which has been followed by a scientific idea, in its long
and slow progress from the position of a probable hypothesis to that of
an established law of nature. Our survey has not taken us into very
attractive regions; it has lain, chiefly, in a land flowing with the
abominable, and peopled with mere grubs and mouldiness. And it may be
imagined with what smiles and shrugs, practical and serious
contemporaries of Redi and of Spallanzani may have commented on the waste
of their high abilities in toiling at the solution of problems which,
though curious enough in themselves, could be of no conceivable utility
to mankind.
Nevertheless, you will have observed that before we had travelled very
far upon our road, there appeared, on the right hand and on the left,
fields laden with a harvest of golden grain, immediately convertible into
those things which the most solidly practical men will admit to have
value--viz., money and life.
The direct loss to France caused by the Pébrine in seventeen years cannot
be estimated at less than fifty millions sterling; and if we add to this
what Redi's idea, in Pasteur's hands, has done for the wine-grower and
for the vinegar-maker, and try to capitalise its value, we shall find
that it will go a long way towards repairing the money losses caused by
the frightful and calamitous war of this autumn. And as to the equivalent
of Redi's thought in life, how can we over-estimate the value of that
knowledge of the nature of epidemic and epizootic diseases, and
consequently of the means of checking, or eradicating them, the dawn of
which has assuredly commenced?
Looking back no further than ten years, it is possible to select three
(1863, 1864, and 1869) in which the total number of deaths from scarlet-
fever alone amounted to ninety thousand. That is the return of killed,
the maimed and disabled being left out of sight. Why, it is to be hoped
that the list of killed in the present bloodiest of all wars will not
amount to more than this! But the facts which I have placed before you
must leave the least sanguine without a doubt that the nature and the
causes of this scourge will, one day, be as well understood as those of
the Pébrine are now; and that the long-suffered massacre of our innocents
will come to an end.
And thus mankind will have one more admonition that "the people perish
for lack of knowledge"; and that the alleviation of the miseries, and the
promotion of the welfare, of men must be sought, by those who will not
lose their pains, in that diligent, patient, loving study of all the
multitudinous aspects of Nature, the results of which constitute exact
knowledge, or Science. It is the justification and the glory of this
great meeting that it is gathered together for no other object than the
advancement of the moiety of science which deals with those phenomena of
nature which we call physical. May its endeavours be crowned with a full
measure of success!
IX
GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE
[1862]
Merchants occasionally go through a wholesome, though troublesome and not
always satisfactory, process which they term "taking stock." After all
the excitement of speculation, the pleasure of gain, and the pain of
loss, the trader makes up his mind to face facts and to learn the exact
quantity and quality of his solid and reliable possessions.
The man of science does well sometimes to imitate this procedure; and,
forgetting for the time the importance of his own small winnings, to re-
examine the common stock in trade, so that he may make sure how far the
stock of bullion in the cellar--on the faith of whose existence so much
paper has been circulating--is really the solid gold of truth.
The Anniversary Meeting of the Geological Society seems to be an occasion
well suited for an undertaking of this kind--for an inquiry, in fact,
into the nature and value of the present results of palaeontological
investigation; and the more so, as all those who have paid close
attention to the late multitudinous discussions in which palaeontology is
implicated, must have felt the urgent necessity of some such scrutiny.
First in order, as the most definite and unquestionable of all the
results of palaeontology, must be mentioned the immense extension and
impulse given to botany, zoology, and comparative anatomy, by the
investigation of fossil remains. Indeed, the mass of biological facts has
been so greatly increased, and the range of biological speculation has
been so vastly widened, by the researches of the geologist and
palaeontologist, that it is to be feared there are naturalists in
existence who look upon geology as Brindley regarded rivers. "Rivers,"
said the great engineer, "were made to feed canals;" and geology, some
seem to think, was solely created to advance comparative anatomy.
Were such a thought justifiable, it could hardly expect to be received
with favour by this assembly. But it is not justifiable. Your favourite
science has her own great aims independent of all others; and if,
notwithstanding her steady devotion to her own progress, she can scatter
such rich alms among her sisters, it should be remembered that her
charity is of the sort that does not impoverish, but "blesseth him that
gives and him that takes."
Regard the matter as we will, however, the facts remain. Nearly 40,000
species of animals and plants have been added to the Systema Naturae by
palaeontological research. This is a living population equivalent to that
of a new continent in mere number; equivalent to that of a new
hemisphere, if we take into account the small population of insects as
yet found fossil, and the large proportion and peculiar organisation of
many of the Vertebrata.