When we see that a weak solution of sulphuric acid is capable of disengaging from the blood the scent of the animal, we shall then bear in mind that this odorous emanation contains particles of all the scents peculiar to each tissue and organ of the animal.  When we further say that each organ in a living animal draws by selective affinity from the blood those materials which are necessary for its sustenance, we must not forget that each organ draws at the same time by a similar selective affinity the specific odorous substances requisite for its constructive requirements.

We have now only to suppose that the embryonal germ contains, like the blood itself, all the odorous substances pertaining to the various tissues and organs of the parent, and we shall understand which is the moving principle in the germ that evolves an offspring, shaped in the image and after the likeness of the parents.

In plants it is the blossom which is entrusted with the function of reproduction, and the odorous emanations accompanying that process are well known.  There is strong reason to believe that something similar prevails in the case of animals, as may be seen from an examination of what embryologists call the aura seminalis.

Let us now inquire what the effects are of odours generated in the outer world on animals.  The odorous impressions produced may be pleasant or unpleasant, pleasant to one and unpleasant to another animal.  What is it that constitutes this sensation of pleasure or displeasure?  Professor Yaeger answers, It is harmony or disharmony which makes all the difference.  The olfactory organs of each animal are impregnated by its own specific scent.  Whenever the odorous waves of a substance harmonize in their vibration with the odorous waves emanating from the animal; in other words, whenever they fall in and agree with each other, an agreeable sensation is produced; whenever the reverse takes places, the sensation is disagreeable.  In this way it is that the odour regulates the choice of the food on the part of the animal.  In a similar way the sympathies and antipathies between the various animals are regulated.  For every individual has not only its specific but also its individual scent.  The selection between the sexes, or what, in the case of the human race, is called love, has its mainspring in the odorous harmony subsisting in the two individuals concerned.

This individual scent—­a variation of the specific odorous type—­alters (within the limits of its speciality) with age, with the particular mode of occupation, with the sex, with certain physiological conditions and functions during life, with the state of health, and last, but not least, with the state of our mind.