1 02 Disease and Immunity 



cover. Assuming that the disease is new to the 

 community in the sense that it has not been 

 present for a considerable number of years, 

 there are three things which enter into the 

 proposition. The first is the resisting power of 

 the individual as measured in his general energy 

 supply which may be called upon to combat the 

 disease. The second is the virulence of the par- 

 ticular strain of parasites producing the disease. 

 And the third involves the magnitude of the at- 

 tack as represented by the number of parasites 

 which initially gain entrance or are produced 

 before the system rouses itself to repel the un- 

 expected attack. 



Those persons who die during the epidemic 

 are those who have become previously weakened, 

 and who are subjected to a very heavy attack. 

 Those who are ill for a time and then recover are 

 those who are weakened to a less extent or who 

 became inoculated with fewer bacteria. 



In any epidemic, many persons appear to 

 escape attack entirely, but frequently this must 

 be more of appearance than of reality. Given a 

 normally healthy person bitten by a single insect 

 which inoculates him with only a few pathologi- 



