Disgust is connected with conservation; it is “an instinctive feeling of protection.” In order to justify this statement, the author passes in review the various objects in nature, noting those which inspire us with disgust, and inquiring into the cause of this. The inorganic kingdom, in general, leaves us indifferent; yet sulphuretted hydrogen, ammonia, and various other gases cause a marked repulsion. This is the effect of an association of ideas; the smell recalls that of decomposition, of a corpse. As regards the vegetable kingdom, the herbivora, by reason of their diet, are the best subjects for observation; their instinct scarcely ever deceives them in the choice of food. We are reminded that, on their arrival in the New World, the Spaniards, hesitating before an unknown flora, whose properties were unknown to them, trusted the judgment of their horses. In man, Richet attributes the repellent influence exerted by bitter aromas to the fact that they frequently co-exist with toxic properties; he takes as types the vegetable alkaloids (quinine, nicotine, etc.), whose power as poisons is in some degree proportioned to their bitterness. So that we have always, at bottom, “the love of life and the horror of death.” In the animal kingdom disgust is aroused by putrescent matter, which indicates or suggests cadaveric decomposition and toxic substances; by parasites, by animals really venomous, or so reputed; for instinct, which sees everything in mass, confounds in the same repugnance the toad and the frog, the venomous serpent and the harmless snake. In its general bearing, the thesis of the finality of disgust is incontestable. There are, no doubt, many exceptions, many facts difficult to explain (some have been pointed out by Richet); but if we take into account the complexity of the question, all objections fall to the ground.