478 



disease — that is 127 out of 220 — recognised that year in the 

 whole State. This bad pre-eminence has, in fact, been since 

 maintained, this asylum containing 63 per cent, of the 408 cases 

 known to occur in Illinois during the twenty-six months preceding 

 the first of September 1911. 



In the year 191 1 but little could be done on this subject ; 

 but beginning with April 1912, a continuous programme of 

 observations, collections, and breeding-cage studies has been 

 steadily maintained, and is still in progress on the Illinois 

 River, and a careful survey has been made of the surroundings 

 of the six insane hospitals of the State, and of the alms- 

 house of the county in which the city of Chicago is situated. 

 Cases of pellagra have occurred in all these institutions during 

 the above-mentioned period, but in widely different ratios to 

 the total number of inmates in each — the Peoria asylum, for 

 example, containing, in 1909, twelve times as many cases per 

 thousand inmates as did any other institution in the State. It 

 thus became a matter of special interest to know the facts in 

 detail concerning the occurrence and abundance of Simulium 

 in the immediate neighbourhood and in the general vicinity of 

 all these institutions. 



Besides this work in the field, the insect collections of my 

 office for many years have been carefully examined, and its 

 field notes and accessions records have been sifted for evidence 

 bearing on the species and distribution of Simulium in the State 

 at large ; and the whole body of the American literature of the 

 subject has been critically studied, with some reference also to 

 a considerable list of European articles. 



According to the present state of our knowledge there are 

 approximately seventy species of Simulium on record for the 

 whole world, of which we are known to have but fifteen in the 

 United States of North America. Nine species, or possibly 

 ten — the status of one being uncertain — have been found in 

 Illinois, one of which, S. hirtipes, occurs also in Europe. No 

 other European species has been found on the continent of North 

 America, although S. reptans is reported from Greenland. The 

 slight attention hitherto paid to these insects in America is 

 illustrated by the fact that two of our nine Illinois species — or 

 three of them, if there are ten in the State — are new to science^ 



