successive assumption 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 constitutes 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 constituted by perhaps not more than two or three steps in the Euglena, is as clearly manifested in the multitudinous stages through which the germ of an oak or of a man passes.  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 passing 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.