Hunters not infrequently kill animals with disease, and if more hunters knew enough to recognize the disease there would be more recorded cases. Sick animals are not as likely to be killed by the hunter as healthy ones, as sick animals seek seclusion and do not move about. In many localities of the United States white-tailed deer are infested with the liver-fluke. Trout and other fish in remote mountain streams are found with tapeworms. Round worms and other parasites infest the white rhinoceros in the African forest. In many instances the parasites and the host, when in health, get on very well together; but when the host weakens the parasites may give him the finishing stroke. Though some morbid conditions described in this book are peculiar to captivity, yet it seems reasonable to assume that many of the diseases found in captive animals occur also in the wild. Some of the extinct races of animals may have been wiped out by disease. Captivity causes numerous physical and mental disarrangements. Unaccustomed, unnatural and unvaried food, change of climate and environment, physical and mental degeneration from disuse of muscle and brain, fear, ennui, nostalgia, lack of the exhilaration of chasing and being chased, unsatisfied sexual feeling—all react harmfully on the captive. No captive animals get their natural food; and though some, like the carnivora, may get approximately their natural food, yet they do not get it in the natural way. They have but little variety and may miss elements important to their well-being. They get only certain cuts— muscle and bone; they do not get blood, guts and glands. The lion’s meat is handed to him. He does not tear down his prey; and one result is that the jaws of the captive-bred lion differ decidedly in shape from the jaws of the wild-bred lion. He gets his food regularly, with awful monotony—twelve pounds of meat at 3.30 p.m. day after day; there is no alternation of feasts and fasts, with consequent change in the balance of the body reserves. Some animals, such as caribou, the moose, the black cock, the hoatzin, the koala, do not long survive captivity, because it is impracticable to obtain their natural food. Gastrointestinal disease is the commonest disease of wild animals. Twenty-five per cent. of sick humans in civilized communities also suffer from it. On the other hand, many animals become accustomed to the new diet and thrive on it.