PART I. 



GENERAL PRINCIPLES OF BACTERIOLOGY. 



CHAPTER I. 

 STRUCTURE AND FORM. 



BEFORE one can gain any intelligent conception of 

 the manner in which bacteria affect dairying, it is first 

 necessary to know something of the life history of these 

 organisms in general, how they live, move, and react 

 toward their environment. 



1. What are bacteria? Toadstools, smuts, rusts, 

 and mildews are known to even the casual observer, be- 

 cause they are of such evident size. Their plant-like 

 nature can be readily understood from their general struc- 

 ture and habits of life. The bacteria, however, are so 

 small that, under ordinary 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 organ- 

 isms, 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 ani- 

 mal kingdom continued 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 

 i B. ' 



