318 
by garbage or through sewer leaks, in which case I have noticed that the 
production of malarial mosquitoes is much more reduced than that of the 
non-malarial species. Where drains are left with weedy edges, as in Car- 
bondale, they are a serious menace to the health of the town. Figures 
4 to 6 show the ideal breeding conditions which these drains afford, and 
records of physicians show frequent cases of malaria in houses situated 
close to them. Fig. 6 shows the proximity of one ditch to a city school 
building. 
The Thompson’s Lake (Fig. 10) type of breeding-place is dangerous, 
providing there is sufficient protective growth along the edge to mask 
wave action, since this seems to be detrimental to the development of 
mosquito larvae. I am inclined to think, however, from the past season’s 
experience, that Anopheles larvae prefer shallower water than is found 
even along edges of this lake, and that consequently it is not as important 
as some other breeding-places before mentioned. However, I found at 
least a few Anopheles upon practically every visit, and as there is a long 
shore-line the lake must have some effect on the amount of malaria. 
Prevalence of Mosquitoes and Abundance of Malaria—lIn the fol- 
lowing table I am showing the presence and abundance of the mosquito 
larvae in the breeding-places which I was able to watch fairly continu- 
ously throughout the year. The six terms used to indicate the numbers 
of Anopheles—none, very few, few, moderate numbers, many, and very 
many—are given grades of 0, 1, 2, 3, 4, and 5, respectively, and the data 
for each month are figured separately, the records for the two years be- 
ing combined. This table shows for each month the number of visits at 
which each of the six grades of abundance was found, the average abun- 
dance per visit for each month, and, in the lowest line of the table, the per- 
centages of abundance, taking the highest grade (very many) as the base 
of the computation. In April, for example, the average abundance of 
larvae of malarial mosquitoes was 2.7 per cent. of “very many ;” in May 
this average was 30.8 per cent.; in June, 67; and so on. 
It was found impossible to obtain accurate figures on the prevalence 
of malaria in Carbondale, but from the medical record of the Illinois 
Central Railroad employees in town, kept by Dr. H. C. Mitchell, division 
surgeon, it is evident that the increase and decrease of the number of 
cases of malaria are closely correlated with the abundance and scarcity 
of the Anopheles mosquitoes. 
Species.—The accompanying table (C) contains a list of the species 
of mosquitoes which were either taken as adults, or bred to the adult stage 
from larvae and pupae, during the last two seasons. It also shows the 
types of breeding-places in which they were found and the months in 
which the collections were made. The numbers used are those of the fore- 
going description of types, viz.: Class I, cattail swamps; Class II, marsh; 
Class III, ponds; Class IV, roadside ditches ; Class V, streams; Class VI, 
open drains; Class VII, lakes. 
y 
