1 88 MANUAL OF BACTERIOLOGY. 



derived from bacterial cultures, suggested the idea that similar 

 ptomaines, formed by the action of bacteria in the living 

 body, might account for the symptoms of many of the infec- 

 tious diseases. The ptomaines were most readily studied 

 because of the comparative facility with which they could be 

 isolated in e condition of purity, where their exact chemical 

 nature could be determined. They were found to be basic 

 compounds derived from nitrogenous material. 



A similar group of substances called leucomaines has been 

 discovered, which are formed within the body by faulty 

 metabolism and not by the action of the bacteria. 



Further study demonstrated, however, that the characteristic 

 features of the infectious diseases are not due to ptomaines, but 

 to toxins. The term toxin, unless otherwise specially desig- 

 nated, applies to extracellular toxins, of which the toxin of 

 diphtheria and that of tetanus are the types; indeed, the only 

 representatives so far obtained are from bacteria, though there 

 are other bodies of a similar nature found in certain plants 

 and in snake and other venom from animals. Toxins have 

 not been obtained yet in a pure state, and consequently 

 their exact chemical character has not been determined; 

 but much has been learned in regard to their physiological 

 actioii, and more information in this direction is constantly 

 being obtained by experiments. They have very marked 

 characteristics and they do not act like ordinary poisons, but 

 behave as if they had the power of reproduction. An o-rdinary 

 poison, such as arsenic, strychnia and the like, begins to act as 

 soon as it is absorbed — there is no period of incubation. The 

 toxins, on the contrary, have a distinct period of incubation. 

 If an animal is given a fatal dose of arsenic or strychnia, it 

 succumbs within a comparatively short time; it is at most a 

 matter of a few hours. But if an animal is injected with a fatal 

 dose of the toxin of tetanus it takes some time, often several 

 days, before anv symptoms develop, and moreover the ani- 



