CHAPTER I. 



STRUCTURE OF THE BACTERIA AND CON- 

 DITIONS GOVERNING THEIR DEVELOP- 

 MENT AND DISTRIBUTION* 



BEFORE one can gain any intelligent conception of the 

 manner in which bacteria affect dairying, it is first neces- 

 sary to know something of the life history of these organ- 

 isms in general, how they live, move and react toward their 

 environment. 



Nature of Bacteria. Toadstools, smuts, rusts and mil- 

 dews are known to even the casual observer, because they 

 are of evident size. Their plant-like nature can be more 

 readily understood from their general structure and habits 

 of life. The bacteria, however, are so small, that under ordi- 

 nary conditions, they only become evident to our unaided 

 senses by the by-products of their activity. 



When Leeuwenhoek (pronounced Lave-en-hake) in 1675 

 first discovered these tiny, rapidly-moving organisms he 

 thought they were animals. Indeed, under a microscope, 

 many of them bear a close resemblance to those minute 

 worms found in vinegar that are known as " vinegar-eels." 

 The idea that they belonged to the animal kingdom con- 

 tinued to hold ground until after the middle of the present 

 century; but with the improvement in microscopes, a more 

 thorough study of these tiny structures was made possible, 

 and their vegetable nature demonstrated. The bacteria as 

 a class are separated from the fungi mainly by their method 

 of growth; from the lower algae by the absence of chloro- 

 phyll, the green coloring matter of vegetable organisms. 



