February, '13] BRUES: STABLE FLY AND INFANTILE PARALYSIS 103 



addition there are undoubtedly many mild, atypical or abortive cases 

 which are difficult of diagnosis. Of the remaining 83-88 per cent, 

 about 25 per cent, recover entirely, some very quickly and a few others 

 only after a number of months, while about 60 per cent remain perma- 

 nently crippled in varying degrees. Children under six years of age 

 are most commonly affected, approximately two thirds of the cases 

 falling into this period. Adult cases are far less frequent, but here 

 the mortality is correspondingly higher, and there is less likelihood of 

 regained muscular control in non-fatal cases. Poliomyelitis is difficult 

 to recognize in its earlier stages, for the preparalytic functional dis- 

 turbances are not ordinarily at all commensurate with the grave 

 nature of the disease. Prognosis is equally difficult, owing to the 

 subsequent very erratic course of the infection. 



On account of its greater prevalence in the Scandinavian peninsula 

 and in Germany, it has been suggested that poliomyelitis was intro- 

 duced into America from one of these European countries. However 

 this may be, during the last seven or eight years our own country has 

 suffered more than any other, although the increased prevalence of 

 the disease here has been paralleled in parts of Europe, and outbreaks 

 have occurred in the West Indies, in Australia, and in other parts of 

 the world. For several years prior to our entomological work, there 

 had been a growing suspicion among those familiar with the disease, 

 that poliomyelitis like several other epidemic diseases, might be insect- 

 borne. Since no data had been collected with this possibility directly 

 in mind, it was necessary to determine a number of points by means 

 of the direct observation of a large series of cases, before it was possible 

 definitely to suspect any particular insect as a probable carrier. How- 

 ever, from previously made studies on the epidemiology of the disease, 

 it appeared that many facts suggested some relation between insects 

 and poliomyelitis. 



Cases usually appear sporadically and very frequently in such a 

 way as to render it very difficult to explain their origin on the basis 

 of infection by personal contact. They also show a seasonal distri- 

 bution very different from what might be expected of a contact in- 

 fection. In winter the disease almost disappears, at the time when 

 children are in closest association both in schools and elsewhere, but 

 rapidly increases in prevalence during the summer, in late June and 

 July, to a maximum in August, then rapidly decreases in September 

 and October to the very slight winter incidence. Geographically, 

 again, poliomyelitis does not follow the hues of densest population, 

 but is on the contrary, quite generally typical of rural, or at least 

 semi-rural districts. Thus in Massachusetts, in 1909, of the cities 

 and towns where the disease occurred, the twenty-five most affected 



