RACE SUSCEPTIBILITY 127 



the question may be simply that of providing the 

 largest number of breeding places, and, reasoning from 

 the analogy of fleas and rats, this seems to be the 

 simplest explanation. 



The black race has been said to enjoy a remarkable 

 immunity. This is, however, far from the case. The 

 greatest observers have pointed out how time and time 

 again they suffer equally with the white races ; the 

 most recent epidemic in Barbados is an example of 

 this. Examples are also cited by Blair and in the 

 1852 Commission's Report. 



From the earliest times yellow fever has been 

 described as the disease of the unacclimatised, the 

 disease of the new arrival ; for that very reason it was 

 thought that as every new arrival must sooner or later 

 get it, the sooner it was got o\ er the better, and with 

 this kind of reasoning the native inhabitants folded 

 their arms and did nothing. It was the young soldiers 

 and merchants who suffered in the old days, and to-day 

 in many parts of the world, as in the Amazon, it is tlie 

 young merchants who fall to the disease. 



The explanation is that the native, be he black or 

 white, has no natural immunity, but he has acquired 

 immunity through having had an attack of the disease, 

 most probably in childhood. He survives, and is in conse- 

 quence immune. When, therefore, a case of yellow fever 

 is imported into a district and infects the stegomyias, 

 those who succumb are naturally the non-immunes, 

 that is, the new arrivals. But let it be now observed 

 that with the increase of sanitation and the diminution 

 of mosquitos, brought about as described in a previous 



