Distribution of Bacteria, 69 



or the wall cell thickens and encloses the proto- 

 plasm. In the spore condition the bacteria are in- 

 active, but are able to endure much greater extremes 

 of heat, cold or moisture than when active. When 

 the conditions of growth become again favorable, the 

 spore again becomes active, or is said to germinate, 

 and the vital processes are resumed. 



Bacteria are widely distributed through nature. 

 In fact, there are very few places where they may 

 not be found. They are so light and small that 

 they float readily in the atmosphere, particularly when 

 accompanied by particles of dust. They are found 

 in all rivers and streams, upon the surface of the 

 earth, and upon all organic matter. In fact, they 

 are universally distributed. By far the larger num- 

 ber are not only perfectly harmless but positively 

 beneficial. They serve to transform dead organic 

 matter into its original condition, and so act as 

 scavengers. Others, like the milk ferments, bring 

 about specific changes in some definite substances, 

 while still others, a large class, are the specific 

 causes of various diseases in men and animals. 



Presence of bacteria in milk. — In ordinary milk, 

 bacteria are always present in large numbers. These 

 gain access to the milk from the atmosphere, from 

 the bodies of the animal and the milker, through 

 contact with the vessels into which the milk is 

 drawn, and to some extent through the udder of the 

 animal. The milk when secreted is sterile. So 

 far as is known, no bacteria can pass through the 

 digestive organs and blood vessels of the animal 



