THE INFLUENCE OF URBAN AND RURAL ENVIRONMENT 373 



throat, a chief determining factor is the frequence and 

 intimacy of personal contact, especially if this is uncon- 

 trollable, as in the stores, conveyances, pubhc streets, 

 eating places, and industries of many cities. From the 

 experience of the United States it would appear that the 

 acute communicable diseases of childhood are acquired 

 earher in life in cities, that they cause a higher death rate 

 for this very reason among children and that adult city 

 populations are more generally immune to measles, mumps 

 diphtheria and scarlet fever than are country people of the 

 same ages. 



It has been noted in army experience in many countries, 

 in the course of enhstment for obhgatory routine mihtary 

 training, and in the emergency of mobihzationi for w^ar, 

 that young men from the cities are less likely to develop 

 the acute communicable diseases than are those coming 

 from rural regions. Only recently has the science of immu- 

 nology advanced to the point v^here proof of immunity can 

 be given, in tv^o of the diseases in question, i.e., diphtheria 

 and scarlet fever, and it is found that the prevalence of 

 immunity to these diseases is greater among city children 

 than in rural children even when there has been no history 

 of attacks of the diseases in question. There is good cir- 

 cumstantial evidence to suggest that by the very process 

 of widespread exposure to those contacts through which 

 communicable diseases are spread, many children in cities 

 acquire, possibly through unrecognized mild attacks of 

 infection and carrier stages, an active and fairly permanent, 

 if not absolute, immunity, which serves as an important 

 protection to them earher in hfe and more commonly than 

 to children relatively isolated in rural households who meet 

 a smaller play and school and work group. In other words, 

 there are some compensations in the form of immunity 

 for the higher death rates for these diseases now generally 

 recorded in urban communities. 



In spite of our inadequate reporting of the venereal 

 diseases and the uncertainty as to certificate of deaths 

 from these causes, all the experience with both white and 

 colored populations in the United States tends to show 

 their much wider prevalence and higher mortahty in cities 



