fifteen hundred years ago, the child of any well-to-do Roman citizen was
taught just these same things; reading and writing in his own, and,
perhaps, the Greek tongue; the elements of mathematics; and the
religion, morality, history, and geography current in his time.
Furthermore, I do not think I err in affirming that, if such a Christian
Roman boy, who had finished his education, could be transplanted into
one of our public schools, and pass through its course of instruction,
he would not meet with a single unfamiliar line of thought; amidst all
the new facts he would have to learn, not one would suggest a different
mode of regarding the universe from that current in his own time.
And yet surely there is some great difference between the civilisation
of the fourth century and that of the nineteenth, and still more between
the intellectual habits and tone of thought of that day and this?
And what has made this difference? I answer fearlessly--The prodigious
development of physical science within the last two centuries.
CCXV
Modern civilisation rests upon physical science; take away her gifts to
our own country, and our position among the leading nations of the world
is gone to-morrow; for it is physical science only that makes
intelligence and moral energy stronger than brute force.
CCXVI
The whole of modern thought is steeped in science; it has made its way
into the works of our best poets, and even the mere man of letters, who
affects to ignore and despise science, is unconsciously impregnated with
her spirit, and indebted for his best products to her methods. I believe
that the greatest intellectual revolution mankind has yet seen is now
slowly taking place by her agency. She is teaching the world that the
ultimate court of appeal is observation and experiment, and not
authority; she is teaching it to estimate the value of evidence; she is
creating a firm and living faith in the existence of immutable moral and
physical laws, perfect obedience to which is the highest possible aim of
an intelligent being.
But of all this your old stereotyped system of education takes no note.
Physical science, its methods, its problems, and its difficulties, will
meet the poorest boy at every turn, and yet we educate him in such a
manner that he shall enter the world as ignorant of the existence of the
methods and facts of science as the day he was born. The modern world is
full of artillery; and we turn out our children to do battle in it,
equipped with the shield and sword of an ancient gladiator.
CCXVII
Posterity will cry shame on us if we do not remedy this deplorable state
of things. Nay, if we live twenty years longer, our own consciences will
cry shame on us.
It is my firm conviction that the only way to remedy it is to make the
elements of physical science an integral part of primary education. I
have endeavoured to show you how that may be done for that branch of
science which it is my business to pursue; and I can but add, that I
should look upon the day when every schoolmaster throughout this land
was a centre of genuine, however rudimentary, scientific knowledge as an
epoch in the history of the country.
But let me entreat you to remember my last words. Addressing myself to
you, as teachers, I would say, mere book learning in physical science is
a sham and a delusion--what you teach, unless you wish to be impostors,
that you must first know; and real knowledge in science means personal
acquaintance with the facts, be they few or many.
CCXVIII
The first distinct enunciation of the hypothesis that all living matter
has sprung from pre-existing living matter came from a contemporary,
though a junior, of Harvey, a native of that country, fertile in men
great in all departments of human activity, which was to intellectual
Europe, in the sixteenth and seventeenth centuries, what Germany is in
the nineteenth. It was in Italy, and from Italian teachers, that Harvey
received the most important part of his scientific education. And it was
a student trained in the same schools, Francesco Redi--a man of the
widest knowledge and most versatile abilities, distinguished alike as
scholar, poet, physician and naturalist--who, just two hundred and two
years ago,[3] published his "Esperienze intorno alla Generazione degl'
Insetti," and gave to the world the idea, the growth of which it is my
purpose to trace. Redi's book went through five editions in twenty
years; and the extreme simplicity of his experiments, and the clearness
of his arguments, gained for his views and for their consequences,
almost universal acceptance.
[3] These words were written in 1870.
Redi did not trouble himself much with speculative considerations, but
attacked particular cases of what was supposed to be "spontaneous
generation" experimentally. Here are dead animals, or pieces of meat,
says he; I expose them to the air in hot weather, and in a few days they
swarm with maggots. You tell me that these are generated in the dead
flesh; but if I put similar bodies, while quite fresh, into a jar, and
tie some fine gauze over the top of the jar, not a maggot makes its
appearance, while the dead substances, nevertheless, putrefy just in the
same way as before. It is obvious, therefore, that the maggots are not
generated by the corruption of the meat; and that the cause of their
formation must be a something which is kept away by gauze. But gauze
will not keep away aeriform bodies, or fluids. This something must
therefore, exist in the form of solid particles too big to get through
the gauze. Nor is one long left in doubt what these solid particles are;
for the blow-flies, attracted by the odour of the meat, swarm round the
vessel, and, urged by a powerful but in this case misleading instinct,
lay eggs out of which maggots are immediately hatched, upon the gauze.
The conclusion, therefore, is unavoidable; the maggots are not generated
by the meat, but the eggs which give rise to them are brought through
the air by the flies.
These experiments seem almost childishly simple, and one wonders how it
was that no one ever thought of them before. Simple as they are,
however, they are worthy of the most careful study, for every piece of
experimental work since done, in regard to this subject, has been shaped
upon the model furnished by the Italian philosopher. As the results of
his experiments were the same, however varied the nature of the
materials he used, it is not wonderful that there arose in Redi's mind a
presumption that, in all such cases of the seeming production of life
from dead matter, the real explanation was the introduction of living
germs from without into that dead matter. And thus the hypothesis that
living matter always arises by the agency of pre-existing living matter,
took definite shape; and had, henceforward, a right to be considered and
a claim to be refuted, in each particular case, before the production of
living matter in any other way could be admitted by careful reasoners.
It will be necessary for me to refer to this hypothesis so frequently,
that, to save circumlocution, I shall call it the hypothesis of
_Biogenesis_; and I shall term the contrary doctrine--that living matter
may be produced by not living matter--the hypothesis of _Abiogenesis_.
In the seventeenth century, as I have said, the latter was the dominant
view, sanctioned alike by antiquity and by authority; and it is
interesting to observe that Redi did not escape the customary tax upon a
discoverer of having to defend himself against the charge of impugning
the authority of the Scriptures; for his adversaries declared that the
generation of bees from the carcase of a dead lion is affirmed, in the
Book of Judges, to have been the origin of the famous riddle with which
Samson perplexed the Philistines:--
"Out of the eater came forth meat,
And out of the strong came forth sweetness"
CCXIX
The great tragedy of Science--the slaying of a beautiful hypothesis by
an ugly fact.
CCXX
It remains yet in the order of logic, though not of history, to show
that among these solid destructible particles there really do exist
germs capable of giving rise to the development of living forms in
suitable menstrua. This piece of work was done by M. Pasteur in those
beautiful researches which will ever render his name famous; and which,
in spite of all attacks upon them, appear to me now, as they did seven
years ago, to be models of accurate experimentation and logical
reasoning. He strained air through cotton-wool, and found, as Schroeder
and Dusch had done, that it contained nothing competent to give rise to
the development of life in fluids highly fitted for that purpose. But
the important further links in the chain of evidence added by Pasteur
are three. In the first place he subjected to microscopic examination
the cotton-wool which had served as strainer, and found that sundry
bodies clearly recognisable as germs were among the solid particles
strained off. Secondly, he proved that these germs were competent to
give rise to living forms by simply sowing them in a solution fitted for
their development. And, thirdly, he showed that the incapacity of air
strained through cotton-wool to give rise to life was not due to any
occult change effected in the constituents of the air by the wool, by
proving that the cotton-wool might be dispensed with altogether, and
perfectly free access left between the exterior air and that in the
experimental flask. If the neck of the flask is drawn out into a tube
and bent downwards; and if, after the contained fluid has been carefully
boiled, the tube is heated sufficiently to destroy any germs which may
be present in the air which enters as the fluid cools, the apparatus may
be left to itself for any time and no life will appear in the fluid. The
reason is plain. Although there is free communication between the
atmosphere laden with germs and the germless air in the flask, contact
between the two takes place only in the tube; and as the germs cannot
fall upwards, and there are no currents, they never reach the interior
of the flask. But if the tube be broken short off where it proceeds from
the flask, and free access be thus given to germs falling vertically out
of the air, the fluid, which has remained clear and desert for months,
becomes, in a few days, turbid and full of life.
CCXXI
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 muscae_, 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.
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 "Pebrine" 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 reading the Report made by M. de Quatrefages in 1859, it is
exceedingly interesting to observe that his elaborate study of the
Pebrine 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.
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 Pebrine 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 Pebrine, but has received its explanation from the fact
that the disease is the result of the presence of the microscopic
organism, _Panhistophyton_.
CCXXII
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 Pebrine 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 (1870).
And as to the equivalent of Redi's thought in life, how can we
overestimate 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 Pebrine 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.
CCXXIII
I find three, more or less contradictory, systems of geological thought,
each of which might fairly enough claim these appellations, standing
side by side in Britain. I shall call one of them Catastrophism, another
Uniformitarianism, the third Evolutionism; and I shall try briefly to
sketch the characters of each, that you may say whether the
classification is, or is not, exhaustive.
By Catastrophism I mean any form of geological speculation which, in
order to account for the phenomena of geology, supposes the operation of
forces different in their nature, or immeasurably different in power,
from those which we at present see in action in the universe.
The Mosaic cosmogony is, in this sense, catastrophic, because it assumes
the operation of extranatural power. The doctrine of violent upheavals,
_debacles_, and cataclysms in general, is catastrophic, so far as it
assumes that these were brought about by causes which have now no
parallel. There was a time when catastrophism might, pre-eminently, have
claimed the title of "British popular geology"; and assuredly it has yet
many adherents, and reckons among its supporters some of the most
honoured members of this Society.
By Uniformitarianism I mean especially the teaching of Hutton and of
Lyell.
That great though incomplete work, "The Theory of the Earth," seems to
me to be one of the most remarkable contributions to geology which is
recorded in the annals of the science. So far as the not-living world
is concerned, uniformitarianism lies there, not only in germ, but in
blossom and fruit.
If one asks how it is that Hutton was led to entertain views so far in
advance of those prevalent in his time, in some respects; while, in
others, they seem almost curiously limited, the answer appears to me to
be plain.
Hutton was in advance of the geological speculation of his time,
because, in the first place, he had amassed a vast store of knowledge of
the facts of geology, gathered by personal observation in travels of
considerable extent; and because, in the second place, he was thoroughly
trained in the physical and chemical science of his day, and thus
possessed, as much as any one in his time could possess it, the
knowledge which is requisite for the just interpretation of geological
phenomena, and the habit of thought which fits a man for scientific
inquiry.
It is to this thorough scientific training that I ascribe Hutton's
steady and persistent refusal to look to other causes than those now in
operation for the explanation of geological phenomena.
The internal heat of the earth, the elevation and depression of its
crust, its belchings forth of vapours, ashes, and lava, are its
activities, in as strict a sense as are warmth and the movements and
products of respiration the activities of an animal. The phenomena of
the seasons, of the trade winds, of the Gulf-stream, are as much the
results of the reaction between these inner activities and outward
forces as are the budding of the leaves in spring and their falling in
autumn the effects of the interaction between the organisation of a
plant and the solar light and heat. And, as the study of the activities
of the living being is called its physiology, so are these phenomena the
subject-matter of an analogous telluric physiology, to which we
sometimes give the name of meteorology, sometimes that of physical
geography, sometimes that of geology. Again, the earth has a place in
space and in time, and relations to other bodies in both these respects,
which constitute its distribution. This subject is usually left to the
astronomer; but a knowledge of its broad outlines seems to me to be an
essential constituent of the stock of geological ideas.
CCXXIV
All that can be ascertained concerning the structure, succession of
conditions, actions, and position in space of the earth, is the matter
of fact of its natural history. But, as in biology, there remains the
matter of reasoning from these facts to their causes, which is just as
much science as the other, and indeed more; and this constitutes
geological aetiology.
CCXXV
I suppose that it would be very easy to pick holes in the details of
Kant's speculations, whether cosmological, or specially telluric, in
their application. But for all that, he seems to me to have been the
first person to frame a complete system of geological speculation by
founding the doctrine of evolution.
I have said that the three schools of geological speculation which I
have termed Catastrophism, Uniformitarianism, and Evolutionism, are
commonly supposed to be antagonistic to one another; and I presume it
will have become obvious that in my belief, the last is destined to
swallow up the other two. But it is proper to remark that each of the
latter has kept alive the tradition of precious truths.