342 BACTERIOLOGY. 



immunity and thereby prevent disease, may 

 also be used to cure the disease. The same 

 thing holds good of protective inoculations, 

 which were at first used to prevent the break- 

 ing out of disease, or to render an attack of 

 disease more mild. When disease broke out 

 before the protective inoculation had been 

 made, the so-called anticipatory inoculation 

 was sometimes resorted to. Inoculation was 

 performed in the usual way in the hope that 

 an immune condition would develop quickly 

 enough to protect the still uninjured individ- 

 ual. This was practiced, for example, in 

 human small-pox with vaccine, and still more 

 frequently in sheep-pox with ovine. 



Pasteur introduced an entirely new idea. 

 Immunity frequently makes its appearance 

 very quickly. This was regarded erroneously 

 as the manifestation of a specific character, but 

 so far as it has been controlled by subsequent 

 investigations, it seems often to be due merely 

 to the sudden rousing to activity of the normal 

 protective forces of the body by the stimulus 

 of the invasion. On the other hand, the infec- 

 tion, starting from the moment of penetration 

 of the disease germs, requires time to become 

 manifest as a due sequence to the multiplica- 

 tion of the parasites and their formation of 

 poison ; this interval is called the period of in- 



