260 APPLIED BACTERIOLOGY 



when a person who has been vaccinated does contract 

 small-pox the symptoms are always modified. 



The question of vaccination has recently been investigated 

 in this country by a Eoyal Commission. The evidence given 

 before this Commission is wholly in favour of vaccination, 

 which very greatly diminishes the liability to attack by 

 small-pox, and when this does happen the disease is 

 always milder and less fatal. The chief point of interest 

 arising out of the inquiry is that vaccination begins to lose 

 its efficacy after the fifteenth year. It was also proved 

 definitely that revaccination restores protection, and the 

 necessity for this is strongly impressed. It is worthy of 

 note that in Germany, where revaccination is the practice, 

 the mortality from small-pox is practically nil. 



The Distribution and Pathogenesis of Small-pox. — Small- 

 pox has been recognised and dreaded for fully the last two 

 thousand years, and was probably the best-known to the 

 ancients of all the ' ills that flesh is heir to.' While at 

 intervals it spreads widely over the world, it can still be 

 said to be endemic in India and certain parts of Egypt 

 and the Soudan. 



It has been noticed that the mortality from small-pox is 

 greater in England, India, and America during the winter 

 and spring than during the summer and autumn. Soil 

 does not, so far as is at present ascertained, appear to have 

 any influence on its spread. 



A heavier mortality is found among males than females ; 

 both susceptibility and mortality are heavier among the 

 coloured races than among the whites. 



The infection of small-pox, unlike that of most of the 

 other specific fevers, is air-borne for considerable distances, 

 while at the same time we know too little about the specific 

 poison to be able to easily destroy it, so that the disease is 

 one of the most infectious of the specific fevers. The virus 



