I$2 BACTERIOLOGY. 



numbers. In very large quantities bacterial 

 protoplasm or bacterial proteid is, like any 

 heterogeneous foreign proteid, poisonous to 

 animals, as Hueppe has proved experi- 

 mentally to be the case with a whole series 

 of harmless bacteria and various kinds of 

 proteids. Landois, Daremberg and Buchner 

 discovered earlier that the blood-serum of one 

 species of animal destroys the blood-corpuscles 

 of another. For a similar reason, probably, 

 dead cultures of B. prodigiosus or of the hay 

 bacillus kill animals just as surely as dead 

 cultures of pathogenic bacteria, and indeed just 

 as surely as living infectious and toxic bac- 

 teria. In the conduct of experiments, there- 

 fore, it is necessary to consider not only the 

 poison contained in the poisonous culture 

 fluid, which is able to produce its effect after 

 the bacteria have been removed by filtration, 

 but also the quantity of bacterial protoplasm 

 introduced into the body of an animal. The 

 transitions from infection to intoxication, from 

 disease to poisoning, are therefore manifold 

 and various ; and as a matter of fact these 

 phenomena usually occur side by side. 



A small number of bacteria is sufficient for 

 infection. In many cases, experimentally 

 well established, a single germ is able to pro- 

 voke a disease. This is true as regards the 



