But here, as before, I think the distinction has arisen entirely from confusing a transitory imperfection with an essential character. So long as our information concerning them is imperfect, we cla.s.s all objects together according to resemblances which we _feel_, but cannot _define_: we group them round _types_, in short. Thus, if you ask an ordinary person what kinds of animals there are, he will probably say, beasts, birds, reptiles, fishes, insects, &c. Ask him to define a beast from a reptile, and he cannot do it; but he says, things like a cow or a horse are beasts, and things like a frog or a lizard are reptiles. You see _he does_ cla.s.s by type, and not by definition. But how does this cla.s.sification differ from that of the scientific Zoologist? How does the meaning of the scientific cla.s.s-name of "Mammalia" differ from the unscientific of "Beasts"?
Why, exactly because the former depends on a definition, the latter on a type. The cla.s.s Mammalia is scientifically defined as "all animals which have a vertebrated skeleton and suckle their young." Here is no reference to type, but a definition rigorous enough for a geometrician.
And such is the character which every scientific naturalist recognizes as that to which his cla.s.ses must aspire--knowing, as he does, that cla.s.sification by type is simply an acknowledgment of ignorance and a temporary device.
So much in the way of negative argument as against the reputed differences between Biological and other methods. No such differences, I believe, really exist. The subject-matter of Biological science is different from that of other sciences, but the methods of all are identical; and these methods are--
1. _Observation_ of facts--including under this head that _artificial observation_ which is called _experiment_.
2. That process of tying up similar facts into bundles, ticketed and ready for use, which is called _Comparison_ and _Cla.s.sification_,--the results of the process, the ticketed bundles, being named _General propositions_.
3. _Deduction_, which takes us from the general proposition to facts again--teaches us, if I may so say, to antic.i.p.ate from the ticket what is inside the bundle. And finally--
4. _Verification_, which is the process of ascertaining whether, in point of fact, our antic.i.p.ation is a correct one.
Such are the methods of all science whatsoever; but perhaps you will permit me to give you an ill.u.s.tration of their employment in the science of Life; and I will take as a special case, the establishment of the doctrine of the _Circulation of the Blood_.
In this case, _simple observation_ yields us a knowledge of the existence of the blood from some accidental haemorrhage, we will say: we may even grant that it informs us of the localisation of this blood in particular vessels, the heart, &c., from some accidental cut or the like. It teaches also the existence of a pulse in various parts of the body, and acquaints us with the structure of the heart and vessels.
Here, however, _simple observation_ stops, and we must have recourse to _experiment_.
You tie a vein, and you find that the blood acc.u.mulates on the side of the ligature opposite the heart. You tie an artery, and you find that the blood acc.u.mulates on the side near the heart. Open the chest, and you see the heart contracting with great force. Make openings into its princ.i.p.al cavities, and you will find that all the blood flows out, and no more pressure is exerted on either side of the arterial or venous ligature.
Now all these facts, taken together, const.i.tute the evidence that the blood is propelled by the heart through the arteries, and returns by the veins--that, in short, the blood circulates.
Suppose our experiments and observations have been made on horses, then we group and ticket them into a general proposition, thus:--_all horses have a circulation of their blood_.
Henceforward a horse is a sort of indication or label, telling us where we shall find a peculiar series of phaenomena called the circulation of the blood.
Here is our _general proposition_ then.
How and when are we justified in making our next step--a _deduction_ from it?
Suppose our physiologist, whose experience is limited to horses, meets with a zebra for the first time,--will he suppose that his 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 a.s.s. 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 circ.u.mstances; 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 cla.s.s 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 Ha.s.selt happening to examine a transparent animal of this cla.s.s, 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 bye 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 cla.s.s 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.[60]
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 busy 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 t.i.tle "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 a.s.sert, 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 bye. 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 trespa.s.sing 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.