Let us state before all what is to be understood by the smell of a certain animal.  There is the pure, specific smell of the animal, inherent in its flesh, or, as we shall see hereafter, in certain portions of its flesh.  This smell is best perceived when the flesh is gently boiling in water.  The broth thereby obtained contains the specific taste and smell of the animal—­I call it specific, because every species, nay every variety of species, has its own peculiar taste and smell.  Think of mutton broth, chicken broth, fish broth, &c. &c.  I shall call this smell, the specific scent of the animal.  I need not say that the scent of an animal is quite different from all such odours as are generated within its organism, along with its various secretions and excretions:  bile, gastric juice, sweat, &c.  These odours are again different in the different species and varieties of animals.  The cutaneous exhalation of the goat, the sheep, the donkey, widely differ from each other; and a similar difference prevails with regard to all the other effluvia of these animals.  In fact, as far as olfactory experience goes, we may say that the odour of each secretion and excretion of a certain species of animals is peculiar to itself, and characteristically different in the similar products of another species.

By altering the food of an animal we may considerably alter all the above-mentioned odours, scents, as well as smells; yet essentially they will always retain their specific odoriferous type.  All this is matter of strict experience.

Strongly diffusive as all these odorous substances are, they permeate the whole organism, and each of them contributes its share to what in the aggregate constitutes the smell of the living animal.  It is altogether an excrementitious smell tempered by the scent of the animal.  That excrementitious smell we shall henceforth simply call the smell, in contradistinction to the scent of the animal.

To return after this not very pleasant, but nevertheless necessary digression, to our subject.  Professor Yaeger found that blood, treated by an acid, may emit the scent or the smell of the animal, according as the acid is weak or strong.  A strong acid, rapidly disintegrating the blood, brings out the animal’s smell; a weak acid, the animal’s scent.

We see, then, that in every drop of blood of a certain species of animal, and we may as well say, in each of its blood corpuscles, and in the last instance, in each of its molecules, the respective animal species is fully represented, as to its odorant speciality, under both aspects of scent and smell.

We have, then, on the one side, the fact before us that wherever we meet in the animal kingdom with difference of shape, form, and construction, so different as to constitute a class, a genus, or a family of its own, there we meet at the same time with a distinct and specific scent and smell.  On the other hand, we know that these specific odours are invariably interblended with the very life-blood of the animal.  And lastly, we know that these specific odours cannot be accounted for by any agents taken up in the shape of food from the outer world.  We are, then, driven to the conclusion that they are properties of the inner animal; that they, in other words, pertain to the specific protoplasm of the animal concerned.