Some have a far more acute sense of smell than others, and again some men, probably without being more acutely endowed in that way, pay more attention to smells, and use the memory of them in description and conversation. Guy de Maupassant is remarkable as a writer for his abundant introduction of references to agreeable and mysterious perfumes, and also to repulsive odours. But some men certainly have an exceptionally acute sense of smell, and can, on entering an empty room, recognise that such and such a person has been there by the faint traces--not of perfumery carried by the visitor--but of his individual smell or odour. This brings us to one of the most important facts about odorous bodies and the sense of smell, namely, that not only do the various species of animals (and plants) each have their own odour--often difficult or impossible for man, with his aborted olfactory powers, to distinguish--but that every individual has its own special odour. As to how far this can be considered a universal disposition is doubtful. It is probable that the power of discriminating such individual odours is limited (even in the case of dogs, where it is sometimes very highly developed), to a power of discriminating the distinctive smells of the individuals of certain species of animals, and not of every individual of every species. Everyone knows of the wonderful power of the bloodhound in tracking an individual man by his smell, but dogs of other breeds also often possess what seems to us extraordinary powers of the kind. On a pebbly beach I pick up one smooth flint pebble as big as a walnut. It is closely similar to thousands of others lying there. I hold it in my hand without letting my fox-terrier see it, and then I throw it. It drops some eighty yards off among the other pebbles, and I could not myself find it again. But the dog runs forward, notes vaguely by ear and by eye the spot where it strikes, and then commences a systematic circling within about ten yards of the spot. In half a minute he pounces with the utmost assurance on to one selected stone, and brings it to me. It is invariably the stone which had been in my hand, unseen by the dog, thrown by me, and detected by the smell I have communicated to it.