The Origination of Living Beings
T >>
Thomas H. Huxley >> The Origination of Living Beings
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'.