The use of fish as a regular article of diet is very widely spread. Fresh fish is considered by medical men to be more easily digested than the flesh of beasts or birds, and a healthy substitute for the latter. Almost everywhere where fish are eaten, the practice of drying, and often of salting, fish, so as to store them for consumption after an abundant "catch," has grown up, and with it a great liking for the flavours produced by the special chemical changes in the fish arising from salting and drying. Ordinary putrefaction produces very powerful poisons in the flesh of fish. They are known as "ptomaines," and are produced in the flesh of fish more readily that in that of other animals. But the process of drying in the sun or of salting and smoking the fish averts the formation of these poisons. It seems, however, that a diet of dried fish is responsible for a certain kind of poisoning in man, which renders him liable to the attack of the terrible bacillus of leprosy. The leprosy bacillus must get into the body by an abrasion or crack in the skin, through contact with a person already infected. It is known that the lack of fresh vegetable and animal food produces the ulcerated unhealthy condition called "scurvy," and a "scorbutic" state of the body seems to be favourable to the establishment in it of the leprosy bacillus. The substitution of fresh meat and vegetables as a diet in place of dried fish and salted meat has apparently been one of the chief causes of the disappearance not only of "scurvy" but of leprosy from Europe. Leprosy is rapidly becoming extinct in Norway. It still survives in a few localities, and is common in several uncivilized communities in remote regions, such as parts of Africa, India, China, and the Pacific Islands. In an earlier chapter, p. 292, I have referred to the disease known as "scurvy," which has become so uncommon now as to have escaped thorough investigation by modern pathologists. A few marine fish are known which are highly poisonous to any and every man, even when cooked and eaten in a perfectly fresh condition, and there are many individuals who suffer from the "idiosyncrasy," as it is called, of liability to be dangerously poisoned not only by the peculiar and rare fish which are poisonous to every one, but by any and every fish they may eat, or by two or three common kinds only. Thus, some persons are poisoned if they eat lobster or crab, or oysters or mussels, but can tolerate ordinary fish. Others are poisoned, without fail, by mackerel and by grey mullet, but not by sole or salmon. The symptoms resemble those produced in ordinary persons by the "ptomaines" of putrid fish, and seem to be due to the presence even in fresh fish of a kind of ptomaine which some persons cannot destroy by digestion, whilst most persons can do so. It is literally true that "What is one man's meat is another man's poison."