Diseased animals not unfrequently communicate their diseases to man. Thus so called " measly " cattle and pigs contain in the flesh or muscles innumerable small bladders, which are living animals of a low type. When these are taken into the intestines of man without being killed by thorough cooking they begin to grow, and form tape-worms. Another disease, found often in Germany, Russia, and Sweden, is trichinosis, which is caused by eating pork either raw or not properly cooked. Minute worms live in the muscles of the pig, and these, on getting into the intestines of man, begin to breed in enormous numbers; the young worms then pierce the intestines, get into the blood vessels and into the muscles, so causing diarrhoea, fever, pains in the muscles, and even death.

Certain diseases in cattle ought certainly to prevent them being used as food; these are infectious inflammation of the lungs of cattle, cattle plague, and consumption in the cow, smallpox in the sheep, and trichinosis and swine fever in the pig. The milk also of cows affected with foot and mouth disease sometimes causes severe symptoms with very sore mouth and lips, and, rarely, sore hands in children, and it is almost certain that the milk of tubercular (consumptive) cattle will cause consumption in the human being.

Vegetable foods, if putrid and decayed, may cause severe illness, just as may happen with putrid animal food.