20 IMMUNE SERA 



was less the actual destruction wrought by the 

 bacteria directly, than the injury produced by their 

 chemical products that gave rise to the lesions in 

 the infectious diseases. Brieger, especially, was 

 one of the first to direct attention to the probable 

 existence of specific poisons in the bacteria. He 

 isolated a number of well defined chemical sub- 

 stances called ptomaines, most of which were highly 

 toxic. Subsequent study, however, showed that 

 these were not the specific bacterial poisons. The 

 latter, the true toxins are something quite different 

 as we shall see in a moment. Still later other 

 substances were isolated from bacteria, and these 

 were termed toxalbumins. We now know that 

 some of these were identical with the true toxins, 

 but that others were entirely unrelated. 



What then are the true toxins? A number of 

 pathogenic bacteria, when grown in pure culture, 

 produce dissolved poisons in the culture fluid. 

 These poisons are neither ptomaines nor proteid 

 substances; their chemical nature is still absolutely 

 unknown. They are extremely sensitive to exter- 

 nal influences, especially against heat, and in many 

 ways are very analogous to ferments. Physio- 

 logically the toxins are extremely poisonous, far 

 beyond that of any of the ordinary well known 

 poisons, and this poisonous action manifests itself 

 only after a certain latent period known as the 

 period of incubation. Finally one of the funda- 



