Science & Education. Thomas Henry Huxley
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rel="nofollow" href="#ulink_ae4b0bde-172f-577b-b993-9083bfee0d08">2] Of all the strange assertions 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. [3]
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 classification takes place by type and not by definition. [4]
It is said, in short, that a natural-history class is not capable of being defined--that the class Rosaceae, for instance, or the class 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 class are united together only by the circumstance 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 class 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 class by type, and not by definition. But how does this classification differ from that of the scientific Zoologist? How does the meaning of the scientific class-name of "Mammalia" differ from the unscientific of "Beasts"?
Why, exactly because the former depends on a definition, the latter on a type. The class 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 classes must aspire--knowing, as he does, that classification 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 Classification,--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 anticipate from the ticket what is inside the bundle. And finally--
4. Verification, which is the process of ascertaining whether, in point of fact, our anticipation is a correct one.
Such are the methods of all science whatsoever; but perhaps you will permit me to give you an illustration 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 accumulates on the side of the ligature opposite the heart. You tie an artery, and you find that the blood accumulates on the side near the heart. Open the chest, and you see the heart contracting with great force. Make openings into its principal 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, constitute 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 this generalisation 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 generalisations 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 à 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,