This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Ptomaines are substances resembling alkaloids which are formed in the alimentary canal by the decomposition or putrefaction of nitrogenous foods. They may also form in such food outside of the body. This decomposition is the result of the action of certain micro-organisms simultaneously first described by Gautier in France and Selim in Bologna. It is at present believed that the constitutional symptoms observed in many infectious diseases are caused by similar poisons called toxins, which originate in the blood and other tissues of the body through the action of specific germs. The artificial cultivation of micro-organisms has proved that they are capable of forming substances which have distinct physiological actions that are sometimes highly poisonous. Many of these microorganisms flourish in beef juice, milk, and various solutions of nitrogenous material; and in the alimentary canal, when such food is taken, all the most favourable conditions are present for the development of toxins. When the poisonous germs are ingested, their toxins are readily absorbed by the intestinal mucous membrane, and it is probable that ptomaine poisoning would occur very much oftener were it not that the liver, acting as it does as a gateway for the admission of nutritive matter for the body, is capable of destroying many poisons which enter it from the intestines through the branches of the portal vein.
Corroboration of this statement is found in the fact that snake bites of the surface of the body may prove highly poisonous by immediate absorption of toxic material into the circulation, whereas snake poison may be swallowed with impunity, for if it is absorbed from the alimentary canal it is destroyed in the liver before reaching the nervous system.
The same is true of the action of putrefying meat, which in very small quantities may not produce severe gastro-intestinal symptoms or constitutional disturbances, and yet if inoculated through a cut in the finger may cause symptoms of a violent septic character.
Richard (Diseases of Modern Life) reports a fatal case of poisoning from eating tainted hare. The victim had had a small ulcer beneath the tongue for some time, which became gangrenous after eating the meat, and which was the undoubted source of inoculation.