IMMUNITY 65 



In ■ studying this acquired immunity, Pasteur, a 

 French scientist who hved 1822 to 1895, conceived the 

 idea of artificially producing an attack of a given infec- 

 tion in order to protect the individual against another 

 attack. He realized that it was necessary, however, to 

 so control matters that the original attack should run a 

 very mild course and not endanger the life of the indi- 

 vidual. After considerable experimental labor, Pasteur 

 found that this could be accomplished by artificially 

 w^eakening the bacteria with w^hich the original attack 

 of the disease was produced. Subsequently Salmon and 

 Smith, in this country, showed that it was not necessary 

 to produce even a mild attack of the disease by the injec- 

 tion of hving bacteria, but that the injection of dead 

 bacteria would produce an immunity against that par- 

 ticular infection. 



Acquired immunity, whether caused by a previous 

 natural attack of the disease, or artificially by the inocu- 

 lation of bacteria, is always strictly specfic, that is, the 

 protection extends only to the particular disease which 

 has previously occurred or whose germs have previously 

 been injected. An attack of scarlet fever protects only 

 against scarlet fever, but not against measles. Inoculat- 

 ing an individual with typhoid bacilli protects him only 

 against typhoid fever, but not against dysentery, plague, 

 cholera, etc. This acquired immunity is often trans- 

 mitted from mother to offspring, transmission being 

 effected mainly, according to Famulener, through the 

 colostrum. This shows the importance of placing baby 

 to the mother's breast soon after birth. 



Before examining into the nature of this very specific 

 form of immunity, it will be well to call attention to 



