their chemical composition and to a certain extent in their physiological action. The ptomaines have sometimes been called the animal alkaloids. This, however, is misleading, as ptomianes may be formed in vegetable as well as in animal proteins. Their essential difference is to be found in their origin. The ptomaines are decomposition products and largely belong to the aliphatic series, whilst the true plant alkaloids are cyclic compounds and practically all of them pyridin derivatives. Owing to the wide variation in the chemical constitution of the ptomaines no analytical methods are known or possible by which they can be differentiated as a class from the vegetable alkaloids. This is possible in the case of certain ptomaines but not all. As a result of this it is not difficult to see how serious medico-legal problems may arise. It is believed in not a few instances ptomaines have been mistaken for the vegetable alkaloids in chemico-legal analyses.
For our knowledge concerning the ptomaines we are indebted very largely to the investigations of Selmi, Nencki, Gautier and Brieger. Selmi was the first (1874-77) to suggest the name—ptomaine—and in fact the first to announce their true nature and origin. Nencki was the first (1876) to isolate a ptomaine (collidine) in pure form and determine its chemical formula. Gautier has given the best classification of both the ptomaines and leucomaines. To Brieger, however, belongs the credit of isolating the largest number (nearly one half) of the known ptomaines and of giving us the best methods for their determination. Vaughan and Novy in this country have made some valuable researches along this line. As the result of an investigation of a number of cases of cheese poisoning they succeeded in isolating a substance which when administered to animals produced symptoms quite similar to those caused in the human subject by the poisonous cheese. To this they gave the name tyrotoxicon. This poison or one very similar has also been isolated from ice cream and milk. The chemical composition of tyrotoxicon has not as yet been definitely determined.
In foods like cheese and certain sausages which depend for their flavor on the action of certain microorganisms it is not strange that we should at times have the formation of poisonous compounds. The so-called process of "ripening" as applied to food products is in fact a partial putrefaction in which we have as the result of bacterial action the formation of ammonia compounds and amino acids which render the food more palatable. It is therefore not a matter of surprise that we should have at times a condition of "over-ripening" with the formation of chemical compounds of a poisonous character. It is to be borne in mind that ptomaines are not found only as the result of advanced putrefaction. Bather are they the products of the earlier stages of protein decomposition. In advanced putrefaction they may themselves be broken down into more simple compounds. Thus
