14 IMMUNITY IN HEALTH 



1875 (when 27 per cent, of the inhabitants succumbed 

 in the space of three montlis) ;* and the spread of 

 phthisis amongst the South African Kaffirs. Indeed, it 

 is a general rule that the first epidemic of any disease 

 in a community is the most virulent, each successive 

 outbreak conferring certain immunity even on those 

 not apparently attacked by the disease.! 



It has also been recorded by Arctic explorers that 

 after a prolonged healthy sojourn in isolation, the 

 return to civilisation was marked by exceptionally 

 severe colds. It may be recalled, in this connection, 

 that immunity against coryza is of short duration. 

 When there is an outbreak of scarlatina in a family 

 or school, some members will escape the illness though 

 freely exposed to infection. Such children may have 

 experienced a slightly increased redness of the tonsils, 

 but nothing which can fairly be called scarlatina. This 

 subject has been investigated of late years by bacterio- 

 logical methods, and it has been found that many of 

 these ''contact" cases, who have never suffered from 

 an attack of the infectious disease, carry the virulent 

 organisms in their throat's and alimentary canals with 

 apparent impunity. These persons form one class of 

 the so-called "healthy carriers" of infectious diseases 

 which constitute such a difficult problem for the 

 Medical Officer of Health to solve. These immune 

 carriers often outnumber the cases of disease ; in epi- 



* Butler gives an account of the epidemics of measles in Fiji and 

 the Faroe Islands, and refers to similar outbreaks in "virgin soil " on 

 tlie banks of the Amazon, among the natives of Astoria, among the 

 North American Indians, among tlie Hottentots, and among the 

 natives of Tasmania. 



t It is only fair to point out that some of the extra virulence of an 

 epidemic in a " virgin " community may be due to the early picking 

 out of those individuals below the general average of resistance. Later 

 when the most susceptible individuals have suffered from the disease 

 the epidemic becomes less violent. It is, however, unlikely that this 

 factor alone is responsible for the dying down of epidemics. 



