06.12.08
But how does this classification differ from that
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 University Cincinnati-raymond Walters College 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 ones
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_.