40 INFECTION AND IMMUNITY 



difference may be compared to the difference between 

 a tender plant and its seeds to deleterious influences, 

 such as extremes of heat and cold. Thus the spores 

 of certain species of bacilli withstand a boiling tem- 

 perature for several hours, while a temperature of 

 150 Fahr. quickly kills most bacteria in the absence 

 of spores. A similar difference is shown as regards 

 the action of chemical agents. Certain agents, 

 e. g., sulphurous-acid gas and carbolic acid, which 

 are extensively used as disinfectants, have been 

 proved by exact experiments to be quite impotent for 

 the destruction of spores. This being the case, it is 

 advisable, in practical disinfection, always to use an 

 agent which has the power of destroying spores, in 

 those cases in which the exact nature of the disease 

 germ has not been demonstrated. The cholera germ 

 of Koch does not form spores ; and there is good 

 reason to believe that the same is true as regards the 

 germs of yellow fever, of scarlet fever, and of small- 

 pox, which have not yet been demonstrated. This 

 inference is based upon evidence obtained in the prac- 

 tical use of disinfectants, and upon certain facts relat- 

 ing to the propagation of these diseases. 



A second general statement, which is justified by 

 the experimental evidence on record, is, that agents 

 which kill bacteria in a certain amount prevent their 

 multiplication in culture fluids, when present in quan- 



