46 INFECTIOUS AND PARASITIC DISEASES. 



Indeed, the source of the bacteria that are in the air 

 and water is the ground. They are carried by the 

 winds with dust, to which they adhere, and by water 

 flowing over the ground. A fact of great importance 

 to be remembered, however, is that bacteria cannot 

 rise jrofn liquids that contain them even should a strong 

 current of wind blow over the liquid. 



Upon our bodies bacteria are constantly present in 

 large numbers, and in every cavity leading to the exterior, 

 but in the tissues and glands of the healthy person they 

 are never found. The number of bacteria upon the 

 body bears a relationship to the cleanliness of the 

 individual, yet even in the most cleanly they are never 

 absent. 



In the same way the number of bacteria in any locality 

 is likewise related to the number of persons, to the 

 density of population, and to the efficiency of the 

 measures practised in the disposal of waste. Any 

 kind of organic matter, whether it be manure heaps, 

 the waste from kitchens, or the dejecta and secretions 

 of man and animals, furnishes appropriate food for 

 these scavengers. The chief interest for us in this 

 wide distribution of bacteria is the relationship of their 

 presence to man and animals, especially in that it 

 draws attention to the danger of contamination of the 

 ground, the water, and food-stuffs from persons and 

 animals suffering from bacterial diseases, and the 

 spread in consequence of disease in this way. 



