COLLECTION OF STATISTICS. 



91 



are cloudy weather (especially if prolonged), sunny weather, frequent or excessive 

 fogs or dews, amount of rainfall, and frequency of rainfall, snowfall, hail, excessively 

 hot weather, cold spells and frosts, droughts, daily maximum and minimum tem- 

 perature, prevalence of special diseases correlated with special peculiar conditions, 

 absence of other diseases, etc. 



Natural Methods of Infection. 



Under this heading the student should be on the watch for transmission of the 

 disease through fungous or insect injuries, by mollusks, by birds or quadrupeds, 

 and by the hand of man. Man contributes to the spread of diseases in various ways, 



Fig.75.* 



e.g., by neglect to remove diseased plants, by use of infected knives and other 

 tools, by the introduction of infected seeds, or manures, or soils, or water, and by 

 subjecting his plants to a variet)' of depressing and unwholesome conditions. 



A great variety of parasites find their home in the earth, the top crust of which 

 swarms with bacteria and fungi. Such parasites are frequenth' introduced from one 

 locality to another in infected soils adhering to wagons and other farm tools, to the 

 feet of men and animals, to the roots of transported plants, etc. The soil is a living 

 thing and it should not be transported even from one field to another on the same 



*FiG. 75. — Bacterium Stewarti filling the substomatic chamber and pushing out into the deeper 

 tissues of a maize leaf. The result of an inoculation made by placing a small quantity of a pure 

 culture on the tip of a sweet-corn leaf in the seedling stage. For orientation see fig. 74. The glo- 

 bose bodies are nuclei, which are not enlarged (?). 



