90 



SCIENCE 



[N. S. Vol. XXXVII. No. 942 



the inside surfaces of the window-panes of 

 public rooms, such as the offices of liotels. 

 furthermore, we have found biting species of 

 Simulmm breeding and emerging in large 

 numbers, not only in the suburbs and out- 

 skirts of Chicago, but far within the limits of 

 that great city — in the Chicago River, which 

 traverses the city, passing through its most 

 densely populated districts, and also in drain- 

 age ditches beside the streets when these hap- 

 pen to contain streams of running water for 

 a sufficient time in spring. Indeed, it is not 

 too much to say that Simulium may breed in 

 any flowing stream within the city where the 

 water is not offensively foul with sewage and 

 other contaminations. 



Eeasoning from the time of the onset of 

 pellagra in the ease of certain infants born in 

 November and in December, when sand-flies 

 are not abroad in Italy, Dr. Sambon comes to 

 the conclusion that the incubation period in 

 these cases could not have exceeded three 

 weeks, this being the interval to elapse be- 

 tween the time when these infants were first 

 carried out in spring to the fields where they 

 might have been bitten, and the date of the 

 appearance of the rash which was the first 

 symptom of the disease. If this reasoning is 

 sound, and these infantile cases are fair ex- 

 amples of the incubation period of pellagra, 

 then I am troubled to explain the occurrence 

 in Illinois of two asylum cases — both reported 

 as first attacks of the disease — one first mani- 

 fest on the 24th of December, 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 No- 

 vember 5, and these cases consequently seem 

 to have developed some six or seven weeks 

 after any possibility 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 recog- 

 nized. 



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 trailing grass blade, will in 

 many cases be thickly covered — but only on 

 the up-stream side — with the larvas first, and 

 afterward with the pupag, of Simulium. We 

 have even found larvse and pupse, both in 

 great abundance, coating objects on the bot- 

 tom of the river at a distance from the shore 

 and at a depth of nine or ten feet — a point in 

 which our observations differ, 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 Illinois 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 two hundred 

 and fifty-eight new cases in twenty-six 

 months, is on a bluff about a hundred and 

 fifty 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 alms- 

 house 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 cov- 

 ered with prairie grass except where streams 

 were bordered with narrow belts of forest. 



From the foregoing it will be seen that, 

 although in this discussion I have been 

 obliged to take a critical attitude towards the 

 Simulium theory of this disease, our Illinois 

 data are not, by themselves, conclusive either 

 for or against that hypothesis. This is a 

 source of regret to me, although scarcely a 

 disappointment, as one entomologist, working 

 for so short a time and in so limited an area, 

 could scarcely expect to bring this time-worn 



