Thomas Henry Huxley - Lay Sermons, Addresses and Reviews

T >> Thomas Henry Huxley >> Lay Sermons, Addresses and Reviews

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Suppose our physiologist, whose experience is limited to horses, meets
with a zebra for the first time,--will he suppose that this
generalization holds good for zebras also?

That depends very much on his turn of mind. But we will suppose him to
be a bold man. He will say, "The zebra is certainly not a horse, but it
is very like one,--so like, that it must be the 'ticket' or mark of a
blood-circulation also; and, I conclude that the zebra has a
circulation."

That is a deduction, a very fair deduction, but by no means to be
considered scientifically secure. This last quality in fact can only be
given by _verification_--that is, by making a zebra the subject of all
the experiments performed on the horse. Of course, in the present case,
the _deduction_ would be _confirmed_ by this process of verification,
and the result would be, not merely a positive widening of knowledge,
but a fair increase of confidence in the truth of one's generalizations
in other cases.

Thus, having settled the point in the zebra and horse, our philosopher
would have great confidence in the existence of a circulation in the
ass. Nay, I fancy most persons would excuse him, if in this case he did
not take the trouble to go through the process of verification at all;
and it would not be without a parallel in the history of the human mind,
if our imaginary physiologist now maintained that he was acquainted with
asinine circulation _a priori_.

However, if I might impress any caution upon your minds, it is, the
utterly conditional nature of all our knowledge,--the danger of
neglecting the process of verification under any circumstances; and the
film upon which we rest, the moment our deductions carry us beyond the
reach of this great process of verification. There is no better instance
of this than is afforded by the history of our knowledge of the
circulation of the blood in the animal kingdom until the year 1824. In
every animal possessing a circulation at all, which had been observed up
to that time, the current of the blood was known to take one definite
and invariable direction. Now, there is a class of animals called
_Ascidians_, which possess a heart and a circulation, and up to the
period of which I speak, no one would have dreamt of questioning the
propriety of the deduction, that these creatures have a circulation in
one direction; nor would any one have thought it worth while to verify
the point. But, in that year, M. von Hasselt happening to examine a
transparent animal of this class, found to his infinite surprise, that
after the heart had beat a certain number of times, it stopped, and then
began beating the opposite way--so as to reverse the course of the
current, which returned by and by to its original direction.

I have myself timed the heart of these little animals. I found it as
regular as possible in its periods of reversal: and I know no spectacle
in the animal kingdom more wonderful than that which it presents--all
the more wonderful that to this day it remains an unique fact, peculiar
to this class among the whole animated world. At the same time I know of
no more striking case of the necessity of the _verification_ of even
those deductions which seem founded on the widest and safest inductions.

Such are the methods of Biology--methods which are obviously identical
with those of all other sciences, and therefore wholly incompetent to
form the ground of any distinction between it and them.[8]

But I shall be asked at once, Do you mean to say that there is no
difference between the habit of mind of a mathematician and that of a
naturalist? Do you imagine that Laplace might have been put into the
Jardin des Plantes, and Cuvier into the Observatory, with equal
advantage to the progress of the sciences they professed?

To which I would reply, that nothing could be further from my thoughts.
But different habits and various special tendencies of two sciences do
not imply different methods. The mountaineer and the man of the plains
have very different habits of progression, and each would be at a loss
in the other's place; but the method of progression, by putting one leg
before the other, is the same in each case. Every step of each is a
combination of a lift and a push; but the mountaineer lifts more and the
lowlander pushes more. And I think the case of two sciences resembles
this.

I do not question for a moment, that while the Mathematician is busied
with deductions _from_ general propositions, the Biologist is more
especially occupied with observation, comparison, and those processes
which lead _to_ general propositions. All I wish to insist upon is, that
this difference depends not on any fundamental distinction in the
sciences themselves, but on the accidents of their subject-matter, of
their relative complexity, and consequent relative perfection.

The Mathematician deals with two properties of objects only, number and
extension, and all the inductions he wants have been formed and finished
ages ago. He is occupied now with nothing but deduction and
verification.

The Biologist deals with a vast number of properties of objects, and
his inductions will not be completed, I fear, for ages to come; but when
they are, his science will be as deductive and as exact as the
Mathematics themselves.

Such is the relation of Biology to those sciences which deal with
objects having fewer properties than itself. But as the student, in
reaching Biology, looks back upon sciences of a less complex and
therefore more perfect nature; so, on the other hand, does he look
forward to other more complex and less perfect branches of knowledge.
Biology deals only with living beings as isolated things--treats only of
the life of the individual: but there is a higher division of science
still, which considers living beings as aggregates--which deals with the
relation of living beings one to another--the science which _observes_
men--whose _experiments_ are made by nations one upon another, in
battle-fields--whose _general propositions_ are embodied in history,
morality, and religion--whose _deductions_ lead to our happiness or our
misery,--and whose _verifications_ so often come too late, and serve
only

"To point a moral or adorn a tale"--

I mean the science of Society or _Sociology_.

I think it is one of the grandest features of Biology, that it occupies
this central position in human knowledge. There is no side of the human
mind which physiological study leaves uncultivated. Connected by
innumerable ties with abstract science, Physiology is yet in the most
intimate relation with humanity; and by teaching us that law and order,
and a definite scheme of development, regulate even the strangest and
wildest manifestations of individual life, she prepares the student to
look for a goal even amidst the erratic wanderings of mankind, and to
believe that history offers something more than an entertaining chaos--a
journal of a toilsome, tragi-comic march nowhither.

The preceding considerations have, I hope, served to indicate the
replies which befit the two first of the questions which I set before
you at starting, viz. what is the range and position of Physiological
Science as a branch of knowledge, and what is its value as a means of
mental discipline.

Its _subject-matter_ is a large moiety of the universe--its _position_
is midway between the physico-chemical and the social sciences. Its
_value_ as a branch of discipline is partly that which it has in common
with all sciences--the training and strengthening of common sense;
partly that which is more peculiar to itself--the great exercise which
it affords to the faculties of observation and comparison; and I may
add, the _exactness_ of knowledge which it requires on the part of those
among its votaries who desire to extend its boundaries.

If what has been said as to the position and scope of Biology be
correct, our third question--What is the practical value of
physiological instruction?--might, one would think, be left to answer
itself.

On other grounds even, were mankind deserving of the title "rational,"
which they arrogate to themselves, there can be no question that they
would consider, as the most necessary of all branches of instruction for
themselves and for their children, that which professes to acquaint them
with the conditions of the existence they prize so highly--which teaches
them how to avoid disease and to cherish health, in themselves and
those who are dear to them.

I am addressing, I imagine, an audience of educated persons; and yet I
dare venture to assert that, with the exception of those of my hearers
who may chance to have received a medical education, there is not one
who could tell me what is the meaning and use of an act which he
performs a score of times every minute, and whose suspension would
involve his immediate death;--I mean the act of breathing--or who could
state in precise terms why it is that a confined atmosphere is injurious
to health.

The _practical value_ of Physiological knowledge! Why is it that
educated men can be found to maintain that a slaughter-house in the
midst of a great city is rather a good thing than otherwise?--that
mothers persist in exposing the largest possible amount of surface of
their children to the cold, by the absurd style of dress they adopt, and
then marvel at the peculiar dispensation of Providence, which removes
their infants by bronchitis and gastric fever? Why is it that quackery
rides rampant over the land; and that not long ago, one of the largest
public rooms in this great city could be filled by an audience gravely
listening to the reverend expositor of the doctrine--that the simple
physiological phenomena known as spirit-rapping, table-turning,
phreno-magnetism, and by I know not what other absurd and inappropriate
names, are due to the direct and personal agency of Satan?

Why is all this, except from the utter ignorance as to the simplest laws
of their own animal life, which prevails among even the most highly
educated persons in this country?

But there are other branches of Biological Science, besides Physiology
proper, whose practical influence, though less obvious, is not, as I
believe, less certain. I have heard educated men speak with an
ill-disguised contempt of the studies of the naturalist, and ask, not
without a shrug, "What is the use of knowing all about these miserable
animals--what bearing has it on human life?"

I will endeavour to answer that question. I take it that all will admit
there is definite Government of this universe--that its pleasures and
pains are not scattered at random, but are distributed in accordance
with orderly and fixed laws, and that it is only in accordance with all
we know of the rest of the world, that there should be an agreement
between one portion of the sensitive creation and another in these
matters.

Surely then it interests us to know the lot of other animal
creatures--however far below us, they are still the sole created things
which share with us the capability of pleasure and the susceptibility to
pain.

I cannot but think that he who finds a certain proportion of pain and
evil inseparably woven up in the life of the very worms, will bear his
own share with more courage and submission; and will, at any rate, view
with suspicion those weakly amiable theories of the Divine government,
which would have us believe pain to be an oversight and a mistake,--to
be corrected by and by. On the other hand, the predominance of happiness
among living things--their lavish beauty--the secret and wonderful
harmony which pervades them all, from the highest to the lowest, are
equally striking refutations of that modern Manichean doctrine, which
exhibits the world as a slave-mill, worked with many tears, for mere
utilitarian ends.

There is yet another way in which natural history may, I am convinced,
take a profound hold upon practical life,--and that is, by its influence
over our finer feelings, as the greatest of all sources of that pleasure
which is derivable from beauty. I do not pretend that natural-history
knowledge, as such, can increase our sense of the beautiful in natural
objects. I do not suppose that the dead soul of Peter Bell, of whom the
great poet of nature says,--

A primrose by the river's brim,
A yellow primrose was to him,--
And it was nothing more,--

would have been a whit roused from its apathy, by the information that
the primrose is a Dicotyledonous Exogen, with a monopetalous corolla and
central placentation. But I advocate natural-history knowledge from this
point of view, because it would lead us to _seek_ the beauties of
natural objects, instead of trusting to chance to force them on our
attention. To a person uninstructed in natural history, his country, or
sea-side, stroll is a walk through a gallery filled with wonderful works
of art, nine-tenths of which have their faces turned to the wall. Teach
him something of natural history, and you place in his hands a catalogue
of those which are worth turning round. Surely our innocent pleasures
are not so abundant in this life, that we can afford to despise this or
any other source of them. We should fear being banished for our neglect
to that limbo, where the great Florentine tells us are those who, during
this life, "wept when they might be joyful."

But I shall be trespassing unwarrantably on your kindness, if I do not
proceed at once to my last point--the time at which Physiological
Science should first form a part of the Curriculum of Education.

The distinction between the teaching of the facts of a science as
instruction, and the teaching it systematically as knowledge, has
already been placed before you in a previous lecture: and it appears to
me, that, as with other sciences, the _common facts_ of Biology--the
uses of parts of the body--the names and habits of the living creatures
which surround us--may be taught with advantage to the youngest child.
Indeed, the avidity of children for this kind of knowledge, and the
comparative ease with which they retain it, is something quite
marvellous. I doubt whether any toy would be so acceptable to young
children as a vivarium, of the same kind as, but of course on a smaller
scale than, those admirable devices in the Zoological Gardens.

On the other hand, systematic teaching in Biology cannot be attempted
with success until the student has attained to a certain knowledge of
physics and chemistry: for though the phaenomena of life are dependent
neither on physical nor on chemical, but on vital forces, yet they
result in all sorts of physical and chemical changes, which can only be
judged by their own laws.

And now to sum up in a few words the conclusions to which I hope you see
reason to follow me.

Biology needs no apologist when she demands a place--and a prominent
place--in any scheme of education worthy of the name. Leave out the
Physiological sciences from your curriculum, and you launch the student
into the world, undisciplined in that science whose subject-matter
would best develop his powers of observation; ignorant of facts of the
deepest importance for his own and others' welfare; blind to the richest
sources of beauty in God's creation; and unprovided with that belief in
a living law, and an order manifesting itself in and through endless
change and variety, which might serve to check and moderate that phase
of despair through which, if he take an earnest interest in social
problems, he will assuredly sooner or later pass.

Finally, one word for myself. I have not hesitated to speak strongly
where I have felt strongly; and I am but too conscious that the
indicative and imperative moods have too often taken the place of the
more becoming subjunctive and conditional. I feel, therefore, how
necessary it is to beg you to forget the personality of him who has thus
ventured to address you, and to consider only the truth or error in what
has been said.

FOOTNOTES:

[4] "In the third place, we have to review the method of Comparison,
which is so specially adapted to the study of living bodies, and by
which, above all others, that study must be advanced. In Astronomy, this
method is necessarily inapplicable; and it is not till we arrive at
Chemistry that this third means of investigation can be used, and then
only in subordination to the two others. It is in the study, both
statical and dynamical, of living bodies that it first acquires its full
development; and its use elsewhere can be only through its application
here."--COMTE'S _Positive Philosophy_, translated by Miss Martineau.
Vol. i. p. 372.

By what method does M. Comte suppose that the equality or inequality of
forces and quantities and the dissimilarity or similarity of
forms--points of some slight importance not only in Astronomy and
Physics, but even in Mathematics--are ascertained, if not by Comparison?

[5] "Proceeding to the second class of means,--Experiment cannot but be
less and less decisive, in proportion to the complexity of the phaenomena
to be explored; and therefore we saw this resource to be less effectual
in chemistry than in physics: and we now find that it is eminently
useful in chemistry in comparison with physiology. _In fact, the nature
of the phaenomena seems to offer almost insurmountable impediments to any
extensive and prolific application of such a procedure in
biology._"--Comte, vol i. p. 367.

M. Comte, as his manner is, contradicts himself two pages further on,
but that will hardly relieve him from the responsibility of such a
paragraph as the above.

[6] "Nouvelle Fonction du Foie considere comme organe producteur de
matiere sucree chez l'Homme et les Animaux," par M. Claude Bernard.

[7] "_Natural Groups given by Type, not by Definition...._ The class is
steadily fixed, though not precisely limited; it is given, though not
circumscribed; it is determined, not by a boundary-line without, but by
a central point within; not by what it strictly excludes, but what it
eminently includes; by an example, not by a precept; in short, instead
of Definition we have a _Type_ for our director. A type is an example of
any class, for instance, a species of a genus, which is considered as
eminently possessing the characters of the class. All the species which
have a greater affinity with this type-species than with any others,
form the genus, and are ranged about it, deviating from it in various
directions and different degrees."--WHEWELL, _The Philosophy of the
Inductive Sciences_, vol. i. pp. 476, 477.

[8] Save for the pleasure of doing so, I need hardly point out my
obligations to Mr. J.S. Mill's "System of Logic," in this view of
scientific method.

VI.

ON THE STUDY OF ZOOLOGY.

Natural history is the name familiarly applied to the study of the
properties of such natural bodies as minerals, plants, and animals; the
sciences which embody the knowledge man has acquired upon these subjects
are commonly termed Natural Sciences, in contradistinction to other,
so-called "physical," sciences; and those who devote themselves
especially to the pursuit of such sciences have been, and are, commonly
termed "Naturalists."

Linnaeus was a naturalist in this wide sense, and his "Systema Naturae"
was a work upon natural history, in the broadest acceptation of the
term; in it, that great methodizing spirit embodied all that was known
in his time of the distinctive characters of minerals, animals, and
plants. But the enormous stimulus which Linnaeus gave to the
investigation of nature soon rendered it impossible that any one man
should write another "Systema Naturae," and extremely difficult for any
one to become a naturalist such as Linnaeus was.

Great as have been the advances made by all the three branches of
science, of old included under the title of natural history, there can
be no doubt that zoology and botany have grown in an enormously greater
ratio than mineralogy; and hence, as I suppose, the name of "natural
history" has gradually become more and more definitely attached to these
prominent divisions of the subject, and by "naturalist" people have
meant more and more distinctly to imply a student of the structure and
functions of living beings.

However this may be, it is certain that the advance of knowledge has
gradually widened the distance between mineralogy and its old
associates, while it has drawn zoology and botany closer together; so
that of late years it has been found convenient (and indeed necessary)
to associate the sciences which deal with vitality and all its phenomena
under the common head of "biology;" and the biologists have come to
repudiate any blood-relationship with their foster-brothers, the
mineralogists.

Certain broad laws have a general application throughout both the animal
and the vegetable worlds, but the ground common to these kingdoms of
nature is not of very wide extent, and the multiplicity of details is so
great, that the student of living beings finds himself obliged to devote
his attention exclusively either to the one or the other. If he elects
to study plants, under any aspect, we know at once what to call him; he
is a botanist, and his science is botany. But if the investigation of
animal life be his choice, the name generally applied to him will vary,
according to the kind of animals he studies, or the particular phenomena
of animal life to which he confines his attention. If the study of man
is his object, he is called an anatomist, or a physiologist, or an
ethnologist; but if he dissects animals, or examines into the mode in
which their functions are performed, he is a comparative anatomist or
comparative physiologist. If he turns his attention to fossil animals,
he is a palaeontologist. If his mind is more particularly directed to the
description, specific discrimination, classification, and distribution
of animals, he is termed a zoologist.

For the purposes of the present discourse, however, I shall recognise
none of these titles save the last, which I shall employ as the
equivalent of botanist, and I shall use the term zoology as denoting the
whole doctrine of animal life, in contradistinction to botany, which
signifies the whole doctrine of vegetable life.

Employed in this sense, zoology, like botany, is divisible into three
great but subordinate sciences, morphology, physiology, and
distribution, each of which may, to a very great extent, be studied
independently of the other.

Zoological morphology is the doctrine of animal form or structure.
Anatomy is one of its branches, development is another; while
classification is the expression of the relations which different
animals bear to one another, in respect of their anatomy and their
development.

Zoological distribution is the study of animals in relation to the
terrestrial conditions which obtain now, or have obtained at any
previous epoch of the earth's history.

Zoological physiology, lastly, is the doctrine of the functions or
actions of animals. It regards animal bodies as machines impelled by
certain forces, and performing an amount of work, which can be
expressed in terms of the ordinary forces of nature. The final object of
physiology is to deduce the facts of morphology, on the one hand, and
those of distribution on the other, from the laws of the molecular
forces of matter.

Such is the scope of zoology. But if I were to content myself with the
enunciation of these dry definitions, I should ill exemplify that method
of teaching this branch of physical science, which it is my chief
business to-night to recommend. Let us turn away then from abstract
definitions. Let us take some concrete living thing, some animal, the
commoner the better, and let us see how the application of common sense
and common logic to the obvious facts it presents, inevitably leads us
into all these branches of zoological science.

I have before me a lobster. When I examine it, what appears to be the
most striking character it presents? Why, I observe that this part which
we call the tail of the lobster, is made up of six distinct hard rings
and a seventh terminal piece. If I separate one of the middle rings, say
the third, I find it carries upon its under surface a pair of limbs or
appendages, each of which consists of a stalk and two terminal pieces.
So that I can represent a transverse section of the ring and its
appendages upon the diagram board in this way.

If I now take the fourth ring I find it has the same structure, and so
have the fifth and the second; so that, in each of these divisions of
the tail, I find parts which correspond with one another, a ring and two
appendages; and in each appendage a stalk and two end pieces. These
corresponding parts are called, in the technical language of anatomy,
"homologous parts." The ring of the third division is the "homologue"
of the ring of the fifth, the appendage of the former is the homologue
of the appendage of the latter. And, as each division exhibits
corresponding parts in corresponding places, we say that all the
divisions are constructed upon the same plan. But now let us consider
the sixth division. It is similar to, and yet different from, the
others. The ring is essentially the same as in the other divisions; but
the appendages look at first as if they were very different; and yet
when we regard them closely, what do we find? A stalk and two terminal
divisions, exactly as in the others, but the stalk is very short and
very thick, the terminal divisions are very broad and flat, and one of
them is divided into two pieces.

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