BACTERIAL TOXINS 61 



Some bacteria merely multiply in the body and exert their 

 effect simply by their mechanical presence without any 

 peculiar poison. Others have the power of elaborating poisons 

 which are specific or individual a'nd whose effect is added to 

 that of the bacterial bodies. The latter form the larger 

 percentage, and it is with them we shall deal chiefly. The 

 ability of bacteria to cause disease is spoken of as their 

 r/nilt'nci'. Each individual kind of bacterium produces only 

 one form of disease, and always that one form. In the early 

 history of pathological bacteriology Koch elaborated certain 

 rules or postulates by which the relation of bacteria to disease 

 is determined. They are essentially that the same bacterium 

 should always be found in the same clinical disease, produce 

 this disease when injected into animals, be recovered again 

 from the animals, and retain its biological characters. By 

 this means the peculiar expression of bacterial disease has 

 been found, and thus it becomes possible to separate those 

 diseases which are wholly due to the bacteria themselves and 

 those principally arising from the bacterial poisoning. 



Bacterial Toxins. Diphtheria is a disease wherein the 

 bacteria reside and grow on a free surface, such as the pharynx; 

 but their poisons are absorbed and carried in the blood stream, 

 thus producing the peculiar symptoms of the disease. If, 

 however, this toxin is taken, entirely free of diphtheria bacilli, 

 and injected into animals, the same results can be obtained so 

 far as the symptoms are concerned. This is likewise true of 

 tetanus. For the development of typhoid fever and septi- 

 cemia it is necessary that the bacteria themselves should 

 circulate in the blood stream. The reason for this is that 

 while the poisons of the diphtheria bacilli are soluble in fluids 

 and separable from the germs, the poisons of the typhoid 

 bacillus, for instance, remain within the body of the germ and 

 are only effective when the cell dies and disintegrates. The 

 former poisons are called extracellular toxins and the latter 

 infr(treHnIar toxins or cti(1oto.rinft. In practice the word toxin 

 unqualified means extracellular toxins, while intracellular 



