




THE METHOD BY WHICH THE CAUSES OF THE PRESENT AND PAST CONDITIONS OF
ORGANIC NATURE ARE TO BE DISCOVERED.--THE ORIGINATION OF LIVING BEINGS

Lecture III. (of VI.), Lectures To Working Men, at the Museum of
Practical Geology, 1863, On Darwin's work: "Origin of Species".


By Thomas H. Huxley



In the two preceding lectures I have endeavoured to indicate to you the
extent of the subject-matter of the inquiry upon which we are engaged;
and now, having thus acquired some conception of the Past and Present
phenomena of Organic Nature, I must now turn to that which constitutes
the great problem which we have set before ourselves;--I mean, the
question of what knowledge we have of the causes of these phenomena of
organic nature, and how such knowledge is obtainable.

Here, on the threshold of the inquiry, an objection meets us. There are
in the world a number of extremely worthy, well-meaning persons, whose
judgments and opinions are entitled to the utmost respect on account of
their sincerity, who are of opinion that Vital Phenomena, and especially
all questions relating to the origin of vital phenomena, are questions
quite apart from the ordinary run of inquiry, and are, by their very
nature, placed out of our reach. They say that all these phenomena
originated miraculously, or in some way totally different from the
ordinary course of nature, and that therefore they conceive it to be
futile, not to say presumptuous, to attempt to inquire into them.

To such sincere and earnest persons, I would only say, that a question
of this kind is not to be shelved upon theoretical or speculative
grounds. You may remember the story of the Sophist who demonstrated to
Diogenes in the most complete and satisfactory manner that he could not
walk; that, in fact, all motion was an impossibility; and that Diogenes
refuted him by simply getting up and walking round his tub. So, in the
same way, the man of science replies to objections of this kind, by
simply getting up and walking onward, and showing what science has done
and is doing--by pointing to that immense mass of facts which have been
ascertained and systematized under the forms of the great doctrines of
Morphology, of Development, of Distribution, and the like. He sees an
enormous mass of facts and laws relating to organic beings, which
stand on the same good sound foundation as every other natural law; and
therefore, with this mass of facts and laws before us, therefore,
seeing that, as far as organic matters have hitherto been accessible and
studied, they have shown themselves capable of yielding to scientific
investigation, we may accept this as proof that order and law reign
there as well as in the rest of nature; and the man of science says
nothing to objectors of this sort, but supposes that we can and shall
walk to a knowledge of the origin of organic nature, in the same way
that we have walked to a knowledge of the laws and principles of the
inorganic world.

But there are objectors who say the same from ignorance and ill-will. To
such I would reply that the objection comes ill from them, and that the
real presumption, I may almost say the real blasphemy, in this matter,
is in the attempt to limit that inquiry into the causes of phenomena
which is the source of all human blessings, and from which has sprung
all human prosperity and progress; for, after all, we can accomplish
comparatively little; the limited range of our own faculties bounds us
on every side,--the field of our powers of observation is small enough,
and he who endeavours to narrow the sphere of our inquiries is only
pursuing a course that is likely to produce the greatest harm to his
fellow-men.

But now, assuming, as we all do, I hope, that these phenomena are
properly accessible to inquiry, and setting out upon our search into the
causes of the phenomena of organic nature, or, at any rate, setting out
to discover how much we at present know upon these abstruse matters, the
question arises as to what is to be our course of proceeding, and what
method we must lay down for our guidance. I reply to that question,
that our method must be exactly the same as that which is pursued in any
other scientific inquiry, the method of scientific investigation being
the same for all orders of facts and phenomena whatsoever.

I must dwell a little on this point, for I wish you to leave this room
with a very clear conviction that scientific investigation is not, as
many people seem to suppose, some kind of modern black art. I say that
you might easily gather this impression from the manner in which
many persons speak of scientific inquiry, or talk about inductive and
deductive philosophy, or the principles of the "Baconian philosophy."
I do protest that, of the vast number of cants in this world, there are
none, to my mind, so contemptible as the pseudoscientific cant which is
talked about the "Baconian philosophy."

To hear people talk about the great Chancellor--and a very great man he
certainly was,--you would think that it was he who had invented science,
and that there was no such thing as sound reasoning before the time of
Queen Elizabeth. Of course you say, that cannot possibly be true; you
perceive, on a moment's reflection, that such an idea is absurdly wrong,
and yet, so firmly rooted is this sort of impression,--I cannot call it
an idea, or conception,--the thing is too absurd to be entertained,--but
so completely does it exist at the bottom of most men's minds, that this
has been a matter of observation with me for many years past. There
are many men who, though knowing absolutely nothing of the subject with
which they may be dealing, wish, nevertheless, to damage the author of
some view with which they think fit to disagree. What they do, then,
is not to go and learn something about the subject, which one would
naturally think the best way of fairly dealing with it; but they abuse
the originator of the view they question, in a general manner, and wind
up by saying that, "After all, you know, the principles and method
of this author are totally opposed to the canons of the Baconian
philosophy." Then everybody applauds, as a matter of course, and agrees
that it must be so. But if you were to stop them all in the middle of
their applause, you would probably find that neither the speaker nor his
applauders could tell you how or in what way it was so; neither the
one nor the other having the slightest idea of what they mean when they
speak of the "Baconian philosophy."

You will understand, I hope, that I have not the slightest desire to
join in the outcry against either the morals, the intellect, or the
great genius of Lord Chancellor Bacon. He was undoubtedly a very great
man, let people say what they will of him; but notwithstanding all that
he did for philosophy, it would be entirely wrong to suppose that the
methods of modern scientific inquiry originated with him, or with his
age; they originated with the first man, whoever he was; and indeed
existed long before him, for many of the essential processes of
reasoning are exerted by the higher order of brutes as completely and
effectively as by ourselves. We see in many of the brute creation the
exercise of one, at least, of the same powers of reasoning as that which
we ourselves employ.

The method of scientific investigation is nothing but the expression of
the necessary mode of working of the human mind. It is simply the mode
at which all phenomena are reasoned about, rendered precise and
exact. There is no more difference, but there is just the same kind of
difference, between the mental operations of a man of science and those
of an ordinary person, as there is between the operations and methods of
a baker or of a butcher weighing out his goods in common scales, and the
operations of a chemist in performing a difficult and complex analysis
by means of his balance and finely-graduated weights. It is not that
the action of the scales in the one case, and the balance in the other,
differ in the principles of their construction or manner of working; but
the beam of one is set on an infinitely finer axis than the other, and
of course turns by the addition of a much smaller weight.

You will understand this better, perhaps, if I give you some familiar
example. You have all heard it repeated, I dare say, that men of science
work by means of Induction and Deduction, and that by the help of these
operations, they, in a sort of sense, wring from Nature certain other
things, which are called Natural Laws, and Causes, and that out of
these, by some cunning skill of their own, they build up Hypotheses and
Theories. And it is imagined by many, that the operations of the common
mind can be by no means compared with these processes, and that they
have to be acquired by a sort of special apprenticeship to the craft.
To hear all these large words, you would think that the mind of a man of
science must be constituted differently from that of his fellow men; but
if you will not be frightened by terms, you will discover that you are
quite wrong, and that all these terrible apparatus are being used by
yourselves every day and every hour of your lives.

There is a well-known incident in one of Moliere's plays, where the
author makes the hero express unbounded delight on being told that he
had been talking prose during the whole of his life. In the same way, I
trust, that you will take comfort, and be delighted with yourselves, on
the discovery that you have been acting on the principles of inductive
and deductive philosophy during the same period. Probably there is not
one here who has not in the course of the day had occasion to set in
motion a complex train of reasoning, of the very same kind, though
differing of course in degree, as that which a scientific man goes
through in tracing the causes of natural phenomena.

A very trivial circumstance will serve to exemplify this. Suppose you
go into a fruiterer's shop, wanting an apple,--you take up one, and, on
biting it, you find it is sour; you look at it, and see that it is hard
and green. You take up another one, and that too is hard, green, and
sour. The shopman offers you a third; but, before biting it, you examine
it, and find that it is hard and green, and you immediately say that you
will not have it, as it must be sour, like those that you have already
tried.

Nothing can be more simple than that, you think; but if you will take
the trouble to analyze and trace out into its logical elements what
has been done by the mind, you will be greatly surprised. In the first
place, you have performed the operation of Induction. You found that,
in two experiences, hardness and greenness in apples go together with
sourness. It was so in the first case, and it was confirmed by the
second. True, it is a very small basis, but still it is enough to make
an induction from; you generalize the facts, and you expect to find
sourness in apples where you get hardness and greenness. You found upon
that a general law, that all hard and green apples are sour; and that,
so far as it goes, is a perfect induction. Well, having got your natural
law in this way, when you are offered another apple which you find is
hard and green, you say, "All hard and green apples are sour; this
apple is hard and green, therefore this apple is sour." That train of
reasoning is what logicians call a syllogism, and has all its various
parts and terms,--its major premiss, its minor premiss, and its
conclusion. And, by the help of further reasoning, which, if drawn out,
would have to be exhibited in two or three other syllogisms, you arrive
at your final determination, "I will not have that apple." So that, you
see, you have, in the first place, established a law by Induction, and
upon that you have founded a Deduction, and reasoned out the special
conclusion of the particular case. Well now, suppose, having got your
law, that at some time afterwards, you are discussing the qualities
of apples with a friend: you will say to him, "It is a very curious
thing,--but I find that all hard and green apples are sour!" Your friend
says to you, "But how do you know that?" You at once reply, "Oh, because
I have tried it over and over again, and have always found them to be
so." Well, if we were talking science instead of common sense, we should
call that an Experimental Verification. And, if still opposed, you go
further, and say, "I have heard from the people in Somersetshire and
Devonshire, where a large number of apples are grown, that they have
observed the same thing. It is also found to be the case in Normandy,
and in North America. In short, I find it to be the universal experience
of mankind wherever attention has been directed to the subject."
Whereupon, your friend, unless he is a very unreasonable man, agrees
with you, and is convinced that you are quite right in the conclusion
you have drawn. He believes, although perhaps he does not know he
believes it, that the more extensive Verifications are,--that the more
frequently experiments have been made, and results of the same kind
arrived at,--that the more varied the conditions under which the same
results have been attained, the more certain is the ultimate conclusion,
and he disputes the question no further. He sees that the experiment has
been tried under all sorts of conditions, as to time, place, and people,
with the same result; and he says with you, therefore, that the law you
have laid down must be a good one, and he must believe it.

In science we do the same thing;--the philosopher exercises precisely
the same faculties, though in a much more delicate manner. In scientific
inquiry it becomes a matter of duty to expose a supposed law to every
possible kind of verification, and to take care, moreover, that this is
done intentionally, and not left to a mere accident, as in the case of
the apples. And in science, as in common life, our confidence in a law
is in exact proportion to the absence of variation in the result of our
experimental verifications. For instance, if you let go your grasp of
an article you may have in your hand, it will immediately fall to
the ground. That is a very common verification of one of the best
established laws of nature--that of gravitation. The method by which men
of science establish the existence of that law is exactly the same as
that by which we have established the trivial proposition about
the sourness of hard and green apples. But we believe it in such an
extensive, thorough, and unhesitating manner because the universal
experience of mankind verifies it, and we can verify it ourselves at any
time; and that is the strongest possible foundation on which any natural
law can rest.

So much by way of proof that the method of establishing laws in science
is exactly the same as that pursued in common life. Let us now turn
to another matter (though really it is but another phase of the same
question), and that is, the method by which, from the relations of
certain phenomena, we prove that some stand in the position of causes
towards the others.

I want to put the case clearly before you, and I will therefore show you
what I mean by another familiar example. I will suppose that one of you,
on coming down in the morning to the parlour of your house, finds that a
tea-pot and some spoons which had been left in the room on the previous
evening are gone,--the window is open, and you observe the mark of a
dirty hand on the window-frame, and perhaps, in addition to that, you
notice the impress of a hob-nailed shoe on the gravel outside. All these
phenomena have struck your attention instantly, and before two minutes
have passed you say, "Oh, somebody has broken open the window, entered
the room, and run off with the spoons and the tea-pot!" That speech is
out of your mouth in a moment. And you will probably add, "I know there
has; I am quite sure of it!" You mean to say exactly what you know; but
in reality what you have said has been the expression of what is, in all
essential particulars, an Hypothesis. You do not 'know' it at all; it is
nothing but an hypothesis rapidly framed in your own mind! And it is an
hypothesis founded on a long train of inductions and deductions.

What are those inductions and deductions, and how have you got at this
hypothesis? You have observed, in the first place, that the window
is open; but by a train of reasoning involving many Inductions and
Deductions, you have probably arrived long before at the General
Law--and a very good one it is--that windows do not open of themselves;
and you therefore conclude that something has opened the window. A
second general law that you have arrived at in the same way is, that
tea-pots and spoons do not go out of a window spontaneously, and you are
satisfied that, as they are not now where you left them, they have been
removed. In the third place, you look at the marks on the window-sill,
and the shoemarks outside, and you say that in all previous experience
the former kind of mark has never been produced by anything else but
the hand of a human being; and the same experience shows that no other
animal but man at present wears shoes with hob-nails on them such as
would produce the marks in the gravel. I do not know, even if we could
discover any of those "missing links" that are talked about, that they
would help us to any other conclusion! At any rate the law which states
our present experience is strong enough for my present purpose.--You
next reach the conclusion, that as these kinds of marks have not been
left by any other animals than men, or are liable to be formed in any
other way than by a man's hand and shoe, the marks in question have been
formed by a man in that way. You have, further, a general law, founded
on observation and experience, and that, too, is, I am sorry to say, a
very universal and unimpeachable one,--that some men are thieves;
and you assume at once from all these premisses--and that is what
constitutes your hypothesis--that the man who made the marks outside and
on the window-sill, opened the window, got into the room, and stole your
tea-pot and spoons. You have now arrived at a 'Vera Causa';--you have
assumed a Cause which it is plain is competent to produce all the
phenomena you have observed. You can explain all these phenomena only by
the hypothesis of a thief. But that is a hypothetical conclusion, of the
justice of which you have no absolute proof at all; it is only rendered
highly probable by a series of inductive and deductive reasonings.

I suppose your first action, assuming that you are a man of ordinary
common sense, and that you have established this hypothesis to your own
satisfaction, will very likely be to go off for the police, and set
them on the track of the burglar, with the view to the recovery of your
property. But just as you are starting with this object, some person
comes in, and on learning what you are about, says, "My good friend,
you are going on a great deal too fast. How do you know that the man who
really made the marks took the spoons? It might have been a monkey that
took them, and the man may have merely looked in afterwards." You would
probably reply, "Well, that is all very well, but you see it is contrary
to all experience of the way tea-pots and spoons are abstracted; so
that, at any rate, your hypothesis is less probable than mine." While
you are talking the thing over in this way, another friend arrives, one
of that good kind of people that I was talking of a little while ago.
And he might say, "Oh, my dear sir, you are certainly going on a great
deal too fast. You are most presumptuous. You admit that all these
occurrences took place when you were fast asleep, at a time when you
could not possibly have known anything about what was taking place. How
do you know that the laws of Nature are not suspended during the night?
It may be that there has been some kind of supernatural interference in
this case." In point of fact, he declares that your hypothesis is one
of which you cannot at all demonstrate the truth, and that you are by no
means sure that the laws of Nature are the same when you are asleep as
when you are awake.

Well, now, you cannot at the moment answer that kind of reasoning. You
feel that your worthy friend has you somewhat at a disadvantage. You
will feel perfectly convinced in your own mind, however, that you are
quite right, and you say to him, "My good friend, I can only be guided
by the natural probabilities of the case, and if you will be kind enough
to stand aside and permit me to pass, I will go and fetch the police."
Well, we will suppose that your journey is successful, and that by good
luck you meet with a policeman; that eventually the burglar is found
with your property on his person, and the marks correspond to his hand
and to his boots. Probably any jury would consider those facts a very
good experimental verification of your hypothesis, touching the cause
of the abnormal phenomena observed in your parlour, and would act
accordingly.

Now, in this suppositious case, I have taken phenomena of a very common
kind, in order that you might see what are the different steps in an
ordinary process of reasoning, if you will only take the trouble to
analyse it carefully. All the operations I have described, you will
see, are involved in the mind of any man of sense in leading him to
a conclusion as to the course he should take in order to make good a
robbery and punish the offender. I say that you are led, in that case,
to your conclusion by exactly the same train of reasoning as that which
a man of science pursues when he is endeavouring to discover the origin
and laws of the most occult phenomena. The process is, and always must
be, the same; and precisely the same mode of reasoning was employed by
Newton and Laplace in their endeavours to discover and define the causes
of the movements of the heavenly bodies, as you, with your own common
sense, would employ to detect a burglar. The only difference is, that
the nature of the inquiry being more abstruse, every step has to be most
carefully watched, so that there may not be a single crack or flaw in
your hypothesis. A flaw or crack in many of the hypotheses of daily life
may be of little or no moment as affecting the general correctness of
the conclusions at which we may arrive; but, in a scientific inquiry,
a fallacy, great or small, is always of importance, and is sure to be
constantly productive of mischievous, if not fatal results.

Do not allow yourselves to be misled by the common notion that an
hypothesis is untrustworthy simply because it is an hypothesis. It is
often urged, in respect to some scientific conclusion, that, after
all, it is only an hypothesis. But what more have we to guide us in
nine-tenths of the most important affairs of daily life than hypotheses,
and often very ill-based ones? So that in science, where the evidence of
an hypothesis is subjected to the most rigid examination, we may rightly
pursue the same course. You may have hypotheses and hypotheses. A man
may say, if he likes, that the moon is made of green cheese: that is an
hypothesis. But another man, who has devoted a great deal of time and
attention to the subject, and availed himself of the most powerful
telescopes and the results of the observations of others, declares that
in his opinion it is probably composed of materials very similar to
those of which our own earth is made up: and that is also only an
hypothesis. But I need not tell you that there is an enormous difference
in the value of the two hypotheses. That one which is based on sound
scientific knowledge is sure to have a corresponding value; and that
which is a mere hasty random guess is likely to have but little value.
Every great step in our progress in discovering causes has been made
in exactly the same way as that which I have detailed to you. A person
observing the occurrence of certain facts and phenomena asks, naturally
enough, what process, what kind of operation known to occur in nature
applied to the particular case, will unravel and explain the mystery?
Hence you have the scientific hypothesis; and its value will be
proportionate to the care and completeness with which its basis had been
tested and verified. It is in these matters as in the commonest affairs
of practical life: the guess of the fool will be folly, while the guess
of the wise man will contain wisdom. In all cases, you see that the
value of the result depends on the patience and faithfulness with
which the investigator applies to his hypothesis every possible kind of
verification.

I dare say I may have to return to this point by-and-by; but having
dealt thus far with our logical methods, I must now turn to something
which, perhaps, you may consider more interesting, or, at any rate,
more tangible. But in reality there are but few things that can be more
important for you to understand than the mental processes and the means
by which we obtain scientific conclusions and theories. [1] Having
granted that the inquiry is a proper one, and having determined on
the nature of the methods we are to pursue and which only can lead to
success, I must now turn to the consideration of our knowledge of the
nature of the processes which have resulted in the present condition of
organic nature.

Here, let me say at once, lest some of you misunderstand me, that I have
extremely little to report. The question of how the present condition of
organic nature came about, resolves itself into two questions. The first
is: How has organic or living matter commenced its existence? And the
second is: How has it been perpetuated? On the second question I shall
have more to say hereafter. But on the first one, what I now have to say
will be for the most part of a negative character.

If you consider what kind of evidence we can have upon this matter, it
will resolve itself into two kinds. We may have historical evidence and
we may have experimental evidence. It is, for example, conceivable, that
inasmuch as the hardened mud which forms a considerable portion of the
thickness of the earth's crust contains faithful records of the past
forms of life, and inasmuch as these differ more and more as we go
further down,--it is possible and conceivable that we might come to
some particular bed or stratum which should contain the remains of those
creatures with which organic life began upon the earth. And if we did
so, and if such forms of organic life were preservable, we should have
what I would call historical evidence of the mode in which organic life
began upon this planet. Many persons will tell you, and indeed you will
find it stated in many works on geology, that this has been done, and
that we really possess such a record; there are some who imagine that
the earliest forms of life of which we have as yet discovered any
record, are in truth the forms in which animal life began upon the
globe. The grounds on which they base that supposition are these:--That
if you go through the enormous thickness of the earth's crust and get
down to the older rocks, the higher vertebrate animals--the quadrupeds,
birds, and fishes--cease to be found; beneath them you find only the
invertebrate animals; and in the deepest and lowest rocks those remains
become scantier and scantier, not in any very gradual progression,
however, until, at length, in what are supposed to be the oldest rocks,
the animal remains which are found are almost always confined to four
forms--'Oldhamia', whose precise nature is not known, whether plant or
animal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal,
having the same essential plan of construction, though differing in
many details from a lobster or crab; and Hymenocaris, which is also a
crustacean. So that you have all the 'Fauna' reduced, at this period,
to four forms: one a kind of animal or plant that we know nothing about,
and three undoubted animals--two crustaceans and one mollusc.

I think, considering the organization of these mollusca and crustacea,
and looking at their very complex nature, that it does indeed require a
very strong imagination to conceive that these were the first created of
all living things. And you must take into consideration the fact that
we have not the slightest proof that these which we call the oldest beds
are really so: I repeat, we have not the slightest proof of it. When you
find in some places that in an enormous thickness of rocks there are but
very scanty traces of life, or absolutely none at all; and that in other
parts of the world rocks of the very same formation are crowded with the
records of living forms, I think it is impossible to place any reliance
on the supposition, or to feel oneself justified in supposing that these
are the forms in which life first commenced. I have not time here
to enter upon the technical grounds upon which I am led to this
conclusion,--that could hardly be done properly in half a dozen lectures
on that part alone;--I must content myself with saying that I do not at
all believe that these are the oldest forms of life.

I turn to the experimental side to see what evidence we have there.
To enable us to say that we know anything about the experimental
origination of organization and life, the investigator ought to be able
to take inorganic matters, such as carbonic acid, ammonia, water, and
salines, in any sort of inorganic combination, and be able to build them
up into Protein matter, and that that Protein matter ought to begin to
live in an organic form. That, nobody has done as yet, and I suspect it
will be a long while before anybody does do it. But the thing is by no
means so impossible as it looks; for the researches of modern chemistry
have shown us--I won't say the road towards it, but, if I may so say,
they have shown the finger-post pointing to the road that may lead to
it.

It is not many years ago--and you must recollect that Organic Chemistry
is a young science, not above a couple of generations old,--you must not
expect too much of it; it is not many years ago since it was said to be
perfectly impossible to fabricate any organic compound; that is to say,
any non-mineral compound which is to be found in an organized being. It
remained so for a very long period; but it is now a considerable number
of years since a distinguished foreign chemist contrived to fabricate
Urea, a substance of a very complex character, which forms one of the
waste products of animal structures. And of late years a number of other
compounds, such as Butyric Acid, and others, have been added to the
list. I need not tell you that chemistry is an enormous distance from
the goal I indicate; all I wish to point out to you is, that it is by no
means safe to say that that goal may not be reached one day. It may be
that it is impossible for us to produce the conditions requisite to the
origination of life; but we must speak modestly about the matter, and
recollect that Science has put her foot upon the bottom round of the
ladder. Truly he would be a bold man who would venture to predict where
she will be fifty years hence.

There is another inquiry which bears indirectly upon this question,
and upon which I must say a few words. You are all of you aware of the
phenomena of what is called spontaneous generation. Our forefathers,
down to the seventeenth century, or thereabouts, all imagined, in
perfectly good faith, that certain vegetable and animal forms gave
birth, in the process of their decomposition, to insect life. Thus,
if you put a piece of meat in the sun, and allowed it to putrefy, they
conceived that the grubs which soon began to appear were the result
of the action of a power of spontaneous generation which the meat
contained. And they could give you receipts for making various animal
and vegetable preparations which would produce particular kinds of
animals. A very distinguished Italian naturalist, named Redi, took up
the question, at a time when everybody believed in it; among others our
own great Harvey, the discoverer of the circulation of the blood. You
will constantly find his name quoted, however, as an opponent of the
doctrine of spontaneous generation; but the fact is, and you will see it
if you will take the trouble to look into his works, Harvey believed
it as profoundly as any man of his time; but he happened to enunciate a
very curious proposition--that every living thing came from an 'egg'; he
did not mean to use the word in the sense in which we now employ it, he
only meant to say that every living thing originated in a little rounded
particle of organized substance; and it is from this circumstance,
probably, that the notion of Harvey having opposed the doctrine
originated. Then came Redi, and he proceeded to upset the doctrine in a
very simple manner. He merely covered the piece of meat with some very
fine gauze, and then he exposed it to the same conditions. The result
of this was that no grubs or insects were produced; he proved that the
grubs originated from the insects who came and deposited their eggs in
the meat, and that they were hatched by the heat of the sun. By
this kind of inquiry he thoroughly upset the doctrine of spontaneous
generation, for his time at least.

Then came the discovery and application of the microscope to scientific
inquiries, which showed to naturalists that besides the organisms which
they already knew as living beings and plants, there were an immense
number of minute things which could be obtained apparently almost at
will from decaying vegetable and animal forms. Thus, if you took some
ordinary black pepper or some hay, and steeped it in water, you would
find in the course of a few days that the water had become impregnated
with an immense number of animalcules swimming about in all directions.
From facts of this kind naturalists were led to revive the theory
of spontaneous generation. They were headed here by an English
naturalist,--Needham,--and afterwards in France by the learned Buffon.
They said that these things were absolutely begotten in the water of
the decaying substances out of which the infusion was made. It did not
matter whether you took animal or vegetable matter, you had only to
steep it in water and expose it, and you would soon have plenty of
animalcules. They made an hypothesis about this which was a very fair
one. They said, this matter of the animal world, or of the higher
plants, appears to be dead, but in reality it has a sort of dim life
about it, which, if it is placed under fair conditions, will cause it
to break up into the forms of these little animalcules, and they will go
through their lives in the same way as the animal or plant of which they
once formed a part.

The question now became very hotly debated. Spallanzani, an Italian
naturalist, took up opposite views to those of Needham and Buffon, and
by means of certain experiments he showed that it was quite possible to
stop the process by boiling the water, and closing the vessel in which
it was contained. "Oh!" said his opponents; "but what do you know you
may be doing when you heat the air over the water in this way? You may
be destroying some property of the air requisite for the spontaneous
generation of the animalcules."

However, Spallanzani's views were supposed to be upon the right side,
and those of the others fell into discredit; although the fact was
that Spallanzani had not made good his views. Well, then, the subject
continued to be revived from time to time, and experiments were made by
several persons; but these experiments were not altogether satisfactory.
It was found that if you put an infusion in which animalcules would
appear if it were exposed to the air into a vessel and boiled it, and
then sealed up the mouth of the vessel, so that no air, save such as
had been heated to 212 degrees, could reach its contents, that then no
animalcules would be found; but if you took the same vessel and exposed
the infusion to the air, then you would get animalcules. Furthermore, it
was found that if you connected the mouth of the vessel with a red-hot
tube in such a way that the air would have to pass through the tube
before reaching the infusion, that then you would get no animalcules.
Yet another thing was noticed: if you took two flasks containing the
same kind of infusion, and left one entirely exposed to the air, and
in the mouth of the other placed a ball of cotton wool, so that the air
would have to filter itself through it before reaching the infusion,
that then, although you might have plenty of animalcules in the first
flask, you would certainly obtain none from the second.

These experiments, you see, all tended towards one conclusion--that the
infusoria were developed from little minute spores or eggs which
were constantly floating in the atmosphere, which lose their power of
germination if subjected to heat. But one observer now made another
experiment which seemed to go entirely the other way, and puzzled
him altogether. He took some of this boiled infusion that I have been
speaking of, and by the use of a mercurial bath--a kind of trough used
in laboratories--he deftly inverted a vessel containing the infusion
into the mercury, so that the latter reached a little beyond the level
of the mouth of the 'inverted' vessel. You see that he thus had a
quantity of the infusion shut off from any possible communication with
the outer air by being inverted upon a bed of mercury.

He then prepared some pure oxygen and nitrogen gases, and passed them
by means of a tube going from the outside of the vessel, up through the
mercury into the infusion; so that he thus had it exposed to a perfectly
pure atmosphere of the same constituents as the external air. Of course,
he expected he would get no infusorial animalcules at all in that
infusion; but, to his great dismay and discomfiture, he found he almost
always did get them.

Furthermore, it has been found that experiments made in the manner
described above answer well with most infusions; but that if you fill
the vessel with boiled milk, and then stop the neck with cotton-wool,
you 'will' have infusoria. So that you see there were two experiments
that brought you to one kind of conclusion, and three to another; which
was a most unsatisfactory state of things to arrive at in a scientific
inquiry.

Some few years after this, the question began to be very hotly discussed
in France. There was M. Pouchet, a professor at Rouen, a very learned
man, but certainly not a very rigid experimentalist. He published a
number of experiments of his own, some of which were very ingenious, to
show that if you went to work in a proper way, there was a truth in
the doctrine of spontaneous generation. Well, it was one of the most
fortunate things in the world that M. Pouchet took up this question,
because it induced a distinguished French chemist, M. Pasteur, to take
up the question on the other side; and he has certainly worked it out
in the most perfect manner. I am glad to say, too, that he has published
his researches in time to enable me to give you an account of them. He
verified all the experiments which I have just mentioned to you--and
then finding those extraordinary anomalies, as in the case of the
mercury bath and the milk, he set himself to work to discover their
nature. In the case of milk he found it to be a question of temperature.
Milk in a fresh state is slightly alkaline; and it is a very curious
circumstance, but this very slight degree of alkalinity seems to have
the effect of preserving the organisms which fall into it from the
air from being destroyed at a temperature of 212 degrees, which is the
boiling point. But if you raise the temperature 10 degrees when you boil
it, the milk behaves like everything else; and if the air with which
it comes in contact, after being boiled at this temperature, is passed
through a red-hot tube, you will not get a trace of organisms.

He then turned his attention to the mercury bath, and found on
examination that the surface of the mercury was almost always covered
with a very fine dust. He found that even the mercury itself was
positively full of organic matters; that from being constantly exposed
to the air, it had collected an immense number of these infusorial
organisms from the air. Well, under these circumstances he felt that the
case was quite clear, and that the mercury was not what it had appeared
to M. Schwann to be,--a bar to the admission of these organisms; but
that, in reality, it acted as a reservoir from which the infusion was
immediately supplied with the large quantity that had so puzzled him.

But not content with explaining the experiments of others, M. Pasteur
went to work to satisfy himself completely. He said to himself: "If
my view is right, and if, in point of fact, all these appearances of
spontaneous generation are altogether due to the falling of minute germs
suspended in the atmosphere,--why, I ought not only to be able to show
the germs, but I ought to be able to catch and sow them, and produce
the resulting organisms." He, accordingly, constructed a very ingenious
apparatus to enable him to accomplish this trapping of this "germ dust"
in the air. He fixed in the window of his room a glass tube, in the
centre of which he had placed a ball of gun-cotton, which, as you all
know, is ordinary cotton-wool, which, from having been steeped in strong
acid, is converted into a substance of great explosive power. It is also
soluble in alcohol and ether. One end of the glass tube was, of course,
open to the external air; and at the other end of it he placed an
aspirator, a contrivance for causing a current of the external air to
pass through the tube. He kept this apparatus going for four-and-twenty
hours, and then removed the 'dusted' gun-cotton, and dissolved it in
alcohol and ether. He then allowed this to stand for a few hours, and
the result was, that a very fine dust was gradually deposited at
the bottom of it. That dust, on being transferred to the stage of a
microscope, was found to contain an enormous number of starch grains.
You know that the materials of our food and the greater portion of
plants are composed of starch, and we are constantly making use of it in
a variety of ways, so that there is always a quantity of it suspended
in the air. It is these starch grains which form many of those bright
specks that we see dancing in a ray of light sometimes. But besides
these, M. Pasteur found also an immense number of other organic
substances such as spores of fungi, which had been floating about in the
air and had got caged in this way.

He went farther, and said to himself, "If these really are the things
that give rise to the appearance of spontaneous generation, I ought to
be able to take a ball of this 'dusted' gun-cotton and put it into one
of my vessels, containing that boiled infusion which has been kept away
from the air, and in which no infusoria are at present developed, and
then, if I am right, the introduction of this gun-cotton will give rise
to organisms."

Accordingly, he took one of these vessels of infusion, which had been
kept eighteen months, without the least appearance of life, and by a
most ingenious contrivance, he managed to break it open and introduce
such a ball of gun-cotton, without allowing the infusion or the cotton
ball to come into contact with any air but that which had been subjected
to a red heat, and in twenty-four hours he had the satisfaction of
finding all the indications of what had been hitherto called spontaneous
generation. He had succeeded in catching the germs and developing
organisms in the way he had anticipated.

It now struck him that the truth of his conclusions might be
demonstrated without all the apparatus he had employed. To do this, he
took some decaying animal or vegetable substance, such as urine, which
is an extremely decomposable substance, or the juice of yeast, or
perhaps some other artificial preparation, and filled a vessel having a
long tubular neck with it. He then boiled the liquid and bent that
long neck into an S shape or zig-zag, leaving it open at the end. The
infusion then gave no trace of any appearance of spontaneous generation,
however long it might be left, as all the germs in the air were
deposited in the beginning of the bent neck. He then cut the tube close
to the vessel, and allowed the ordinary air to have free and direct
access; and the result of that was the appearance of organisms in it, as
soon as the infusion had been allowed to stand long enough to allow
of the growth of those it received from the air, which was about
forty-eight hours. The result of M. Pasteur's experiments proved,
therefore, in the most conclusive manner, that all the appearances of
spontaneous generation arose from nothing more than the deposition of
the germs of organisms which were constantly floating in the air.

To this conclusion, however, the objection was made, that if that were
the cause, then the air would contain such an enormous number of these
germs, that it would be a continual fog. But M. Pasteur replied that
they are not there in anything like the number we might suppose, and
that an exaggerated view has been held on that subject; he showed that
the chances of animal or vegetable life appearing in infusions, depend
entirely on the conditions under which they are exposed. If they are
exposed to the ordinary atmosphere around us, why, of course, you may
have organisms appearing early. But, on the other hand, if they are
exposed to air from a great height, or from some very quiet cellar, you
will often not find a single trace of life.

So that M. Pasteur arrived at last at the clear and definite result,
that all these appearances are like the case of the worms in the piece
of meat, which was refuted by Redi, simply germs carried by the air and
deposited in the liquids in which they afterwards appear. For my own
part, I conceive that, with the particulars of M. Pasteur's experiments
before us, we cannot fail to arrive at his conclusions; and that the
doctrine of spontaneous generation has received a final 'coup de grace'.

You, of course, understand that all this in no way interferes with the
'possibility' of the fabrication of organic matters by the direct method
to which I have referred, remote as that possibility may be.


[Footnote 1: Those who wish to study fully the doctrines of which I have
endeavoured to give some rough and ready illustrations, must read Mr.
John Stuart Mill's 'System of Logic'.]





