VACCINE OR OPSONIC THERAPY 109. 



The principle by which small-pox vaccine protects 

 is doubtless that of a modified attack of the disease 

 through a diminution of the virulence of the causative 

 germ from passage through an unfavorable host, i. e., 

 the cow. In other words, that cow-pox is a modified 

 form of small-pox, its nature and virulence having been 

 changed by the resistance and general character of the 

 tissues of the cow. So that when a human being is in- 

 oculated with vaccine or cow-pox, he has a mild local 

 disease in place of the widespread general condition 

 which characterizes small-pox. This mild disturbance 

 is sufficient to establish immunity to the disease for a 

 shorter or longer period of time, varying from three or 

 four to fifteen or twenty years. 



The causative germ of small-pox having never been 

 isolated, it is not possible to determine much regarding 

 the mode of action of this product, but years of invariable 

 success and the practical wiping out of small-pox has 

 established its value beyond quibble. 



Preparation. In the preparation of small-pox vaccine 

 young healthy heifers are used. They are carefully ex- 

 amined and tuberculin-tested, and when found healthy 

 are shaved, scrubbed with an antiseptic, and inoculated 

 with cow-pox. The heifers are fed on milk exclusively 

 and kept in separate compartments. When the pus- 

 tules are fully developed at the end of five to seven days, 

 their contents are collected under strict antiseptic con- 

 ditions. The contents of the pustules are mixed with 



