CHAPTER X 



ESSENTIALS OF MILK BACTERIOLOGY 

 By H. W. Hill, M. D. 



nr 



HE Bacteria are very minute living things, which feed 

 ti chiefly on the waste matters of animal and vegetable life, 



""~ and on dead animal and vegetable bodies. There are many- 

 kinds of bacteria, one differing from another in size to 

 some extent, in shape to some extent, but chiefly in the way they 

 live — the kind of food they prefer, the kind of atmosphere they 

 need, the temperature at which they will develop, the products they 

 form from their food, the shape and naked-eye appearance of their 

 mass growths. Hence, although the size and shape of any given 

 bacterium helps towards its recognition, it must be tested in many 

 ways to determine the foods it uses, its effect on its foods, the tem- 

 perature and atmosphere best suited to it, and other details, before 

 any one who examines it can determine its identity. No bacteriol- 

 ogist can recognize what bacterium he is dealing with by merely 

 looking at it with a microscope, except in a very few special cases. 

 The bacteria have no sex. New ones are formed simply by the 

 division of the old ones into two (fission). Size, shape and 

 arrangement, i. e., grouping of individuals in chains, clusters, etc., 

 are studied under the term morphology; the essentials of growth, 

 reproduction, food, chemical products, etc., under physiology. 



Size. — The diameters of the bacteria in general range from 

 about 1/25,000 of an inch (or 1/1000 of a millimeter, which is 



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