This may arise from tainted meat, milk, or fish, more especially shellfish. Ptomaines are alkaloidal substances produced by decomposition, or putrefaction of proteins under the influence of bacterial action. The bacilli specially associated with meat-poisoning include some members of the anaerobic group, e.g. Bacillus botuliuus, which occurs notably in tainted ham and sausages; also bacilli of the protein group, such as Bacillus butyricus, which normally cause putrefaction in wholesome food; and various members of the para-typhoid group, especially the Bacillus entcritidis of Gartner. Serious and even dangerous symptoms - pain, sickness, vomiting, collapse - may arise from eating food tainted as above. In the case of poisoning from eating tainted fish or mussels, the symptoms may arise within an hour or two, and affect mainly the central nervous system. Ptomaine poisoning more commonly arises from eating canned meats which have stood some time after opening. In these cases it may not be easy to determine whether the poison is derived from the tainted meat, or is due to metallic poisoning from ingredients used in the process of tinning. It is well also to keep in view the possibility that it is the result of the "preservative" used. In addition to meat - milk, cream, ice cream, and cheese may also be tainted and induce acute ptomaine poisoning. In connection with ptomaine poisoning, it is important to keep in mind the frequency with which idiosyncrasy is met with to special articles of diet, such as shellfish, strawberries, and the like.
Reference must be made to the occasional occurrence of cases of this kind, e.g., turkey eating deadly nightshade leaves, followed by symptoms of atropine poisoning in the human subject; grouse and hares have been known to be poisoned through eating the tender shoots of the laurel and rhododendron shrubs; oysters similarly may be the cause of typhoid, from being taken from contaminated oyster-beds.
Mouldy flour and unripe grains when old develop poisons from decomposition of their gluten. The more common diseases that are so induced are ergotism and pellagra. The symptoms of ergotism may be of a gangrenous or convulsive character, and are due to the action of the fungus Claviceps purpurea, which grows on rye. Pellagra is a disease of Southern Europe which arises from eating fermented unripe maize or Indian corn made into polenta. It is characterised by an erythema of the skin accompanied by severe mental symptoms. The disease is said to be preventable by the addition of salt to the cornmeal.
Lathyrism is a condition analagous to ergotism and pellagra, but resulting from the adulteration of flour with a grain called the chick-pea vetch; it is met with in India, Italy, and France.
Food sometimes serves as the medium for the introduction of parasites or their embryos, such as tapeworm, roundworm, echinococcus, and trichina. The chief source of infection is the use of raw or imperfectly cooked flesh, a rarer source being the ingestion of vegetables that have been tainted from the excrement of infected animals. Trichinosis is acquired from eating ham or pork infected with the parasites. It may be a serious, and is sometimes a fatal disease.