1913] Charles Frederick Boldiian 259 



infection in general. With this conception of the effects of paren- 

 teral protein cleavage, it is a simple matter to explain the significance 

 of the period of incubation. For those of you who are not medical 

 students, I will say that every infectious disease manifests itself only 

 in a certain period of time after infection has taken place. More- 

 over, this interval is fairly constant. Thus, after a person has con- 

 tracted typhoid fever, some ten to fifteen days elapse before Symp- 

 toms develop. In measles, the incubation is regularly fifteen to 

 eighteen days; in scarlet fever, regularly from three to five days, 

 etc. Formerly this period was explained as the time necessary for 

 the development of germs in sufficient number to produce Symptoms. 

 This explanation was unsatisfactory, because, in artificial in- 

 fections, no matter how large the dose, it was never possible 

 to shorten the incubation period below a certain minimum, and 

 this minimum could not be explained. If, however, we regard in- 

 fecting bacteria as protein introduced parenterally, we shall have no 

 difficulty in explaining the incubation period as the time necessary 

 for the body to develop antibodies which shall act on the bacteria 

 and produce poisonous cleavage products. Even if we do not accept 

 Friedberger's assumption of but a single anaphylatoxin, the same 

 explanation holds for the liberation of endotoxins. In this connec- 

 tion, I ought to say that bacteria invading the body through the in- 

 testinal tract, e. g., the typhoid bacilli, may still be regarded as intro- 

 duced parenterally, because they pass the intestinal barrier and gain 

 access to the other tissues of the body. 



Modern chemotherapy according to Ehrlich. Before leaving 

 the subject of infection and immunity, I should like to say a few 

 words about the chemistry of the cell in relation to chemotherapy. 

 I have already pointed out that Ehrlich holds that the action of a 

 chemical substance on a given cell denotes the existence of definite 

 chemical affinities between the substance and the cell. Applying 

 this conception to the germicidal action of chemicals, he maintains 

 that the latter must have a certain chemical affinity for the parasites 

 in Order to kill them. Substances having such affinities he terms 

 parasitotropic. It is clear, however, that substances which can de- 

 stroy parasites will also be poisonous for the animal body, i. e., they 

 will have chemical affinity for the tissues of the host. They are 



