90 INFECTIOUS AND PARASITIC DISEASES. 



illustration of the altitude the stegomyia may reach is 

 furnished by the history of yellow fever in Mexico, as 

 reported by the U. S. Public Health and Marine- 

 Hospital Service. A commission from this Service, 

 called Working Party No. i, found this mosquito at an 

 altitude of 4200 feet above the sea level, an ascent which 

 they ascribe to a shortening of the time-distance 

 between coast and interior by the building of a railroad. 

 That season and disease are related phe- 



Season. nomena has already been included in our 

 discussion of climate. It only remains to 

 illustrate the relationship. Yellow fever is a disease 

 of tropical countries, and of sub-tropical regions during 

 the warm months; typhoid fever occurs everywhere 

 chiefly in the autumn and early winter months. 



The effect of season upon disease is strikingly shown 

 if we compare the two extremes of the year, summer and 

 winter. The heated term is characterized by diseases 

 affecting the intestinal tract, the cold and blustry 

 months, by affections of the respiratory organs and 

 joints. 



Fasting, poor food, unhygienic surround - 

 Fasting, ings, etc., are potential factors in the pro- 

 PoorFood, duction of infectious diseases. They all 

 Etc. conduce to a low state of the vital forces; 



and an impoverished body falls an easy 

 prey to the pathogenic agents. Nor are the effects 

 of other agencies grouped in our chart under environ- 



