Regarding Physiological Science, then, in its widest sense--as the equivalent of _Biology_--the Science of Individual Life--we have to consider in succession:
1. Its position and scope as a branch of knowledge.
2. Its value as a means of mental discipline.
3. Its worth as practical information.
And lastly,
4. At what period it may best be made a branch of Education.
Our conclusions on the first of these heads must depend, of course, upon the nature of the subject-matter of Biology; and I think a few preliminary considerations will place before you in a clear light the vast difference which exists between the living bodies with which Physiological science is concerned, and the remainder of the universe;--between the phaenomena of Number and s.p.a.ce, of Physical and of Chemical force, on the one hand, and those of Life on the other.
The mathematician, the physicist, and the chemist contemplate things in a condition of rest; they look upon a state of equilibrium as that to which all bodies normally tend.
The mathematician does not suppose that a quant.i.ty will alter, or that a given point in s.p.a.ce will change its direction with regard to another point, spontaneously. And it is the same with the physicist. When Newton saw the apple fall, he concluded at once that the act of falling was not the result of any power inherent in the apple, but that it was the result of the action of something else on the apple. In a similar manner, all physical force is regarded as the disturbance of an equilibrium to which things tended before its exertion,--to which they will tend again after its cessation.
The chemist equally regards chemical change in a as the effect of the action of something external to the body changed. A chemical compound once formed would persist for ever, if no alteration took place in surrounding conditions.
But to the student of Life the aspect of nature is reversed. Here, incessant, and, so far as we know, spontaneous change is the rule, rest the exception--the anomaly to be accounted for. Living things have no inertia, and tend to no equilibrium.
Permit me, however, to give more force and clearness to these somewhat abstract considerations, by an ill.u.s.tration or two.
Imagine a vessel full of water, at the ordinary temperature, in an atmosphere saturated with vapour. The _quant.i.ty_ and the _figure_ of that water will not change, so far as we know, for ever.
Suppose a lump of gold be thrown into the vessel--motion and disturbance of figure exactly proportional to the momentum of the gold will take place. But after a time the effects of this disturbance will subside--equilibrium will be restored, and the water will return to its pa.s.sive state.
Expose the water to cold--it will solidify--and in so doing its particles will arrange themselves in definite crystalline shapes. But once formed, these crystals change no further.
Again, subst.i.tute for the lump of gold some substance capable of entering into chemical relations with the water:--say, a ma.s.s of that substance which is called "protein"--the substance of flesh:--a very considerable disturbance of equilibrium will take place--all sorts of chemical compositions and decompositions will occur; but in the end, as before, the result will be the resumption of a condition of rest.
Instead of such a ma.s.s of _dead_ protein, however, take a particle of _living_ protein--one of those minute microscopic living things which throng our pools, and are known as Infusoria--such a creature, for instance, as an Euglena, and place it in our vessel of water. It is a round ma.s.s provided with a long filament, and except in this peculiarity of shape, presents no appreciable physical or chemical difference whereby it might be distinguished from the particle of dead protein.
But the difference in the phaenomena to which it will give rise is immense: in the first place it will develop a vast quant.i.ty of physical force--cleaving the water in all directions with considerable rapidity by means of the vibrations of the long filament or cilium.
Nor is the amount of chemical energy which the little creature possesses less striking. It is a perfect laboratory in itself, and it will act and react upon the water and the matters contained therein; converting them into new compounds resembling its own substance, and, at the same time, giving up portions of its own substance which have become effete.
Furthermore, the Euglena will increase in size; but this increase is by no means unlimited, as the increase of a crystal might be. After it has grown to a certain extent it divides, and each portion a.s.sumes the form of the original, and proceeds to repeat the process of growth and division.
Nor is this all. For after a series of such divisions and subdivisions, these minute points a.s.sume a totally new form, lose their long tails--round themselves, and secrete a sort of envelope or box, in which they remain shut up for a time, eventually to resume, directly or indirectly, their primitive mode of existence.
Now, so far as we know, there is no natural limit to the existence of the Euglena, or of any other living germ. A living species once launched into existence tends to live for ever.
Consider how widely different this living particle is from the dead atoms with which the physicist and chemist have to do!
The particle of gold falls to the bottom and rests--the particle of dead protein decomposes and disappears--it also rests: but the _living_ protein ma.s.s neither tends to exhaustion of its forces nor to any permanency of form, but is essentially distinguished as a disturber of equilibrium so far as force is concerned,--as undergoing continual metamorphosis and change, in point of form.
Tendency to equilibrium of force and to permanency of form then, are the characters of that portion of the universe which does not live--the domain of the chemist and physicist.
Tendency to disturb existing equilibrium,--to take on forms which succeed one another in definite cycles, is the character of the living world.
What is the cause of this wonderful difference between the dead particle and the living particle of matter appearing in other respects identical?
that difference to which we give the name of Life?
I, for one, cannot tell you. It may be that, by and by, philosophers will discover some higher laws of which the facts of life are particular cases--very possibly they will find out some bond between physico-chemical phaenomena on the one hand, and vital phaenomena on the other. At present, however, we a.s.suredly know of none; and I think we shall exercise a wise humility in confessing that, for us at least, this successive a.s.sumption of different states--(external conditions remaining the same)--this _spontaneity of action_--if I may use a term which implies more than I would be answerable for--which const.i.tutes so vast and plain a practical distinction between living bodies and those which do not live, is an ultimate fact; indicating as such, the existence of a broad line of demarcation between the subject-matter of Biological and that of all other sciences.
For I would have it understood that this simple Euglena is the type of _all_ living things, so far as the distinction between these and inert matter is concerned. That cycle of changes, which is const.i.tuted by perhaps not more than two or three steps in the Euglena, is as clearly manifested in the mult.i.tudinous stages through which the germ of an oak or of a man pa.s.ses. Whatever forms the Living Being may take on, whether simple or complex, _production_, _growth_, _reproduction_, are the phaenomena which distinguish it from that which does not live.
If this be true, it is clear that the student, in pa.s.sing from the physico-chemical to the physiological sciences, enters upon a totally new order of facts; and it will next be for us to consider how far these new facts involve _new_ methods, or require a modification of those with which he is already acquainted. Now a great deal is said about the peculiarity of the scientific method in general, and of the different methods which are pursued in the different sciences. The Mathematics are said to have one special method; Physics another, Biology a third, and so forth. For my own part, I must confess that I do not understand this phraseology.
So far as I can arrive at any clear comprehension of the matter, Science is not, as many would seem to suppose, a modification of the black art, suited to the tastes of the nineteenth century, and flourishing mainly in consequence of the decay of the Inquisition.
Science is, I believe, nothing but _trained and organized common sense_, differing from the latter only as a veteran may differ from a raw recruit: and its methods differ from those of common sense only so far as the guardsman"s cut and thrust differ from the manner in which a savage wields his club. The primary power is the same in each case, and perhaps the untutored savage has the more brawny arm of the two. The _real_ advantage lies in the point and polish of the swordsman"s weapon; in the trained eye quick to spy out the weakness of the adversary; in the ready hand prompt to follow it on the instant. But after all, the sword exercise is only the hewing and poking of the clubman developed and perfected.
So, the vast results obtained by Science are won by no mystical faculties, by no mental processes, other than those which are practised by every one of us, in the humblest and meanest affairs of life. A detective policeman discovers a burglar from the marks made by his shoe, by a mental process identical with that by which Cuvier restored the extinct animals of Montmartre from fragments of their bones. Nor does that process of induction and deduction by which a lady, finding a stain of a peculiar kind upon her dress, concludes that somebody has upset the inkstand thereon, differ in any way, in kind, from that by which Adams and Leverrier discovered a new planet.
The man of science, in fact, simply uses with scrupulous exactness, the methods which we all, habitually and at every moment, use carelessly; and the man of business must as much avail himself of the scientific method--must be as truly a man of science--as the veriest bookworm of us all; though I have no doubt that the man of business will find himself out to be a philosopher with as much surprise as M. Jourdain exhibited, when he discovered that he had been all his life talking prose. If, however, there be no real difference between the methods of science and those of common life, it would seem, on the face of the matter, highly improbable that there should be any difference between the methods of the different sciences; nevertheless, it is constantly taken for granted, that there is a very wide difference between the Physiological and other sciences in point of method.
In the first place it is said--and I take this point first, because the imputation is too frequently admitted by Physiologists themselves--that Biology differs from the Physico-chemical and Mathematical sciences in being "inexact."
Now, this phrase "inexact" must refer either to the _methods_ or to the _results_ of Physiological science.
It cannot be correct to apply it to the methods; for, as I hope to show you by and by, these are identical in all sciences, and whatever is true of Physiological method is true of Physical and Mathematical method.
Is it then the _results_ of Biological science which are "inexact"? I think not. If I say that respiration is performed by the lungs; that digestion is effected in the stomach; that the eye is the organ of sight; that the jaws of a vertebrated animal never open sideways, but always up and down; while those of an annulose animal always open sideways, and never up and down--I am enumerating propositions which are as exact as anything in Euclid. How then has this notion of the inexactness of Biological science come about? I believe from two causes: first, because, in consequence of the great complexity of the science and the mult.i.tude of interfering conditions, we are very often only enabled to predict approximatively what will occur under given circ.u.mstances; and secondly, because, on account of the comparative youth of the Physiological sciences, a great many of their laws are still imperfectly worked out. But, in an educational point of view, it is most important to distinguish between the essence of a science and the accidents which surround it; and essentially, the methods and results of Physiology are as exact as those of Physics or Mathematics.
It is said that the Physiological method is especially _comparative_[4]; and this dictum also finds favour in the eyes of many. I should be sorry to suggest that the speculators on scientific cla.s.sification have been misled by the accident of the name of one leading branch of Biology--_Comparative Anatomy_; but I would ask whether _comparison_, and that cla.s.sification which is the result of comparison, are not the essence of every science whatsoever? How is it possible to discover a relation of cause and effect of _any_ kind without comparing a series of cases together in which the supposed cause and effect occur singly, or combined? So far from comparison being in any way peculiar to Biological science, it is, I think, the essence of every science.
A speculative philosopher again tells us that the Biological sciences are distinguished by being sciences of observation and not of experiment![5]
Of all the strange a.s.sertions into which speculation without practical acquaintance with a subject may lead even an able man, I think this is the very strangest. Physiology not an experimental science! Why, there is not a function of a single organ in the body which has not been determined wholly and solely by experiment. How did Harvey determine the nature of the circulation, except by experiment? How did Sir Charles Bell determine the functions of the roots of the spinal nerves, save by experiment? How do we know the use of a nerve at all, except by experiment? Nay, how do you know even that your eye is your seeing apparatus, unless you make the experiment of shutting it; or that your ear is your hearing apparatus, unless you close it up and thereby discover that you become deaf?
It would really be much more true to say that Physiology is _the_ experimental science _par excellence_ of all sciences; that in which there is least to be learnt by mere observation, and that which affords the greatest field for the exercise of those faculties which characterise the experimental philosopher. I confess, if any one were to ask me for a model application of the logic of experiment, I should know no better work to put into his hands than Bernard"s late Researches on the Functions of the Liver.[6]
Not to give this lecture a too controversial tone, however, I must only advert to one more doctrine, held by a thinker of our own age and country, whose opinions are worthy of all respect. It is, that the Biological sciences differ from all others, inasmuch as in _them_ cla.s.sification takes place by type and not by definition.[7]
It is said, in short, that a natural-history cla.s.s is not capable of being defined--that the cla.s.s Rosaceae, for instance, or the cla.s.s of Fishes, is not accurately and absolutely definable, inasmuch as its members will present exceptions to every possible definition; and that the members of the cla.s.s are united together only by the circ.u.mstance that they are all more like some imaginary average rose or average fish, than they resemble anything else.
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 recognises 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_.