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. 



