THEORIES OF IMMUNITY. 



mucous membranes of well persons, in the hope of 

 producing' a mild case, and thus protecting the 

 individual from an attack of a more malignant 

 form of the disease. 



Jenner's application of his observation in 

 Gloucestershire, where he was born, that dairy- 

 maids handling cows sick with cow-pox ap- 

 peared to be protected against small-pox was 

 the beginning of the stamping out of this great 

 plague in all parts of the civilized world. 



The discovery of the possibility of the attenu- 

 ation of the virulence of a culture on the one 

 hand, and of the possibility of securing an arti- 

 ficial immunity with such attenuated cultures on 

 the other, were more or less the result of chance. 

 Pasteur, with Chamberland and Roux, had been 

 studying the bacillus of chicken-cholera, and 

 interrupted their work during the vacation sea- 

 son of 1879. Upon attempting to resume it 

 they found that their cultures, kept over during 

 the summer, still retained their vitality, but had 

 lost their virulence, either wholly or in great 

 part. (Valery-Radot. La vie de Pasteur, p. 

 427.) Testing the effects of such cultures led 



