CARRIAGE OF DISEASE 
147 
A most careful and thoroughly scientific study of 
the seasonal prevalence of typhoid has been made by 
Sedgwick and Winslow (1902). Their investigation 
included an examination of the published data for all 
countries. They conclude that the increase of typhoid 
with a gradual rise in the mean air temperature is so 
widespread and significant as to indicate an undoubted 
relationship. There is no doubt that a similar rise of 
temperature hastens the rapidity of breeding of the 
house fly until at the culmination of the heated term 
they are present in countless numbers, as we have seen. 
This fact was fully appreciated by Sedgwick and Win¬ 
slow, who in their conclusions use the following words: 
“Of the three great intermediaries of typhoid trans¬ 
mission, fingers, food, and flies, the last is even more 
significant than the others in relation to seasonal varia¬ 
tion. * * * There can be little doubt that many of 
the so-called ‘sporadic’ cases of typhoid fever, which 
are so difficult for the sanitarian to explain, are con¬ 
ditioned by the passage of a fly from an infected vault 
to an unprotected table or an open larder. The relation 
of this factor to the season is of course close and com¬ 
plete : and a certain amount of the autumnal excess of 
fever is undoubtedly traceable to the presence of large 
numbers of flies and to the opportunities for their per¬ 
nicious activity.” 
The real explanation, according to these authors, of 
the seasonal variations of typhoid fever is a direct ef¬ 
fect of temperature upon the persistence in nature of 
germs which proceed from previous victims of disease. 
