104 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. & 



showed an incidence ranging from 5.26 to 1.12 per thousand (averag- 

 ing 1.94), the average population of these places being 3,294; the 

 twenty-five least affected showed an incidence of from .15 to .012 

 per thousand, (averaging .098) and had an average population of 

 32,217. Complete data concerning many other regions are difficult 

 to collocate, but the greater rural incidence seems to Vje an established 

 fact. The significance of this distribution becomes very great when 

 we consider the fact that both domestic animals and the majority of 

 insect species are most abundant over the same areas where polio- 

 myelitis appears in its most extensive outbreaks. 



With these, and other considerations of minor importance in mind, 

 it became possible to draw some tentative conclusions which might 

 be strengthened or disposed of by the actual examination of the en- 

 vironment of a series of cases. 



As a matter of fact, members of nearly all groups of insects which 

 by their life-history seem suited to play a part in the dissemination of 

 disease, have been implicated either as specific or contaminative car- 

 riers of disease in man or the higher mammals. The seasonal distri- 

 bution of poliomyelitis makes it evident at once that insects like fleas, 

 which are known to carry plague; lice which transmit typhus fever; 

 or bedbugs, which are suspected of distributing kala-azar fever, could 

 hardly account for the high summer incidence and practical winter 

 disappearance of poliomyelitis. They vary somewhat in abundance 

 with the progression of the seasons, but are nevertheless quite prevalent 

 all through the winter. Mosquito-borne diseases of course, show a 

 very decided ajstival periodicity, but at least in the case of yellow 

 fever, malarial fever and dengue, spread very rapidly in epidemic 

 form, involving a much greater percentage of the population of a 

 community. This is quite to be expected, on account of the general 

 abundance of mosquitoes and their great persistence in search for 

 human blood. For this reason they enjoy great opportunities of in- 

 fection in the presence of a case of one of these diseases, and exhibit 

 a corresponding activity in distributing the organisms later among 

 other persons. Thus, while poliomyelitis appears in truly epidemic 

 form, it has never developed into extensive outbreaks, comparable 

 with those of mosquito-borne diseases. There appeared, however, 

 no very decided reason why some relatively rare mosquito might not 

 be concerned, except that the summer abundance of poliomyelitis 

 does not show any regular relation to rainfall or to general mosquito 

 prevalence. Ticks are known to act as vectors for a number of diseases, 

 but on account of their method of attachment to the skin of the host 

 for considerable periods, are very noticeable, and in none of the cases, 

 visited could we demonstrate the occurrence of a tick bite, either by 



