296 BACTERIOLOGY. 



certain specific diseases rests in perfect con- 

 fidence that he will not again contract the 

 disease. It is true, the hygienist must ac- 

 knowledge the fact that this good fortune falls 

 to the lot of only a portion of those who have 

 had the disease, and that even this fraction 

 often gain it at the expense of long illness, 

 loss of work and other injurious consequences. 

 From this point of view it is certainly prefer- 

 able, considering all things, not to contract 

 infectious diseases at all. 



The very old observation that protection 

 against a disease may be acquired by endur- 

 ing an attack of that disease has led some 

 mothers to adopt the practice of exposing their 

 healthy children to small-pox, scarlet fever and 

 measles, with the expectation that the children 

 when thus exposed intentionally and artifici- 

 ally to the infection will contract the disease 

 in a milder form than the more susceptible 

 children who have previously sickened in a 

 natural way, but that the children thus delib- 

 erately infected will gain the same amount of 

 protection as the others. Thucydides recom- 

 mended that those who had recovered from the 

 plague at Athens, and had thereby acquired 

 protection, should be employed in the care of 

 the sick. In India and China the custom of 

 blowing into the nostrils dried and pulverized 



