_The Excretions._—There is also a marked difference in the excretory products of the various animals. While, in the carnivora, the action of the urine is acid, it is alkaline in the herbivora (or should be). In man it is frequently acid—though this varies with the nature of the food. Thus, if the diet be largely one of flesh, the urine will become far more acid, and will also become very offensive; the perspiration will also be tainted, and very noticeable to those with a keen sense of smell, and who do not eat meat themselves! This has frequently been observed, and may account for the fact that flesh-eating animals will always eat a horse or a sheep in preference to man, if it be possible. Doubtless, their keen sense of smell detects the fact that man is (usually) largely carnivorous in his habits, and their instinct teaches them that the flesh of the purely herbivorous animal is for this reason superior to that of man. Has anyone thought why it is that a cat will kill a mouse, _and eat it_, while a dog will kill a cat, but will _not_ eat it? It is because the mouse is a vegetarian animal, and the cat is a carnivorous animal. Instinct teaches the cat that the tissues of the mouse’s body are more or less pure and inoffensive—owing to the nature of the diet; while the same instinct teaches the dog that the cat’s body is impure and more or less poisonous, for the reason that _its_ flesh is tainted and full of poisons, because of its diet. If any animal lives upon flesh, that animal’s body is bound to be tainted more or less in consequence; and those animals which prey upon others know that fact, by reason of their sense of smell and instinct. This is a remarkable and most instructive fact; a rule which will rarely be found to fail. Its significance and interpretation is obvious. Professor Schlickeysen also informs us that “the overloading of the blood with flesh-food causes, in order to effect their decomposition, an excessive consumption of oxygen, and hence the difficulty of breathing, and asthmatical affections of many flesh-eaters, and their excessive excretion of carbonic acid.” I have referred to some of these poisons, formed within the system, and the harm they must doubtless exert upon the organism, elsewhere.