446 



SANITATION 



and introduced this "vaccine virus" under the skin of a 

 man. He thus found that he could produce in the man an 

 immunity to the disease. Vaccination (Fig. 310) usually 



FIG. 310. Prosress of Smallpox In Prussia Before and After the Enforce- 

 ment of General Vaccination. Death Rate per 100,000 of Population, 1846 to 

 1886. From "Hygiene of Transmissible Diseases," by Abbott, after Schulz. 



produces a mild inflammation at the place where the 

 virus is introduced; this is due to the growth of the germs. 

 The germs from the cow are so much weaker than those 

 that come from a human smallpox patient that they can- 

 not produce the dreaded disease, but their presence in 



