484 



cases — both reported as first attacks of the disease — one first 

 manifest on December 24th, and the other on the 31st of that 

 month, after a period of three or four weeks of severe cold weather. 

 Our latest Illinois collections of Simulium adults made in any year 

 were obtained November 5th, and these cases consequently 

 seem to have developed some six or seven weeks after any possi- 

 bility of infection by means of Simulium bites. It is possible, 

 however, that this discrepancy is only apparent, and that these 

 were not new cases, arising in the asylum, but recurrent attacks 

 of a disease originating outside and not previously recognised. 



Simulium does not require, with us, swift-running streams 

 for its development, some of the species, at least, breeding in 

 any freely flowing water where the surface is broken into a 

 ripple by depending or projecting objects. A stout weed growing 

 from the bottom of a stream near its margin, or a twig bending 

 down and dipping into the water from the shore, or even a trail- 

 ing grass blade, will in many cases be thickly covered —but only 

 on the up-stream side — with the larvae first, and afterward with 

 the pupee, of Simulium. We have even found larvae and pupae, 

 both, in great abundance, coating objects on the bottom of the 

 river at a distance from the shore and at a depth of nine or ten 

 feet — a point in which our observations difíer, so far as I know, 

 from any others on record. 



In Italy pellagra is said by Sambon to be essentially a disease 

 of mountain valleys ; but if this rule applied in America, we 

 should have only imported cases of pellagra in any part of Illi- 

 nois, or indeed within hundreds of miles of its borders. There 

 is, in fact, no common topographic feature distinguishing the 

 three principal seats of pellagra in our State. The Peoria asylum, 

 with 258 new cases in twenty-six months, is on a blufí about 

 150 feet in height beside one of our largest rivers ; the Elgin 

 asylum, with thirty-eight new cases in the same time, is on a 

 more sloping bank, less than half as high, beside a much smaller 

 stream ; and the Dunning almshouse is on a level, open plain, 

 with no water in its vicinity except a small drainage ditch, which 

 often goes dry in midsummer. The country surrounding all 

 these hospitals is a level or slightly rolling plain, originally covered 

 with prairie grass except where streams were bordered with 

 narrow belts of forest. 



