INTRODUCTION. 



Bacteriology is the youngest member of the sisterhood of 

 those biological sciences that deal with life in its varied man- 

 ifestations and functions. While it has a strictly scientific 

 side, this subject has a greater practical bearing than is found 

 in many of its sister sciences. For a long time is was merely 

 a protege of medicine; even now, the term bacteria is nearly 

 always associated in the minds of many with some dread con- 

 tagious disease, but with further study, the effect of bacteria 

 in many other practical lines is becoming better known, and 

 the circle of its influence is steadily widening. 



Its methods have revolutionized the brewing industries; 

 on the presence of bacteria depends the success or failure of 

 many of the industrial arts, such as butter and cheese-making, 

 many of the operations in tanning, the manufacture of vine- 

 gar, of wines, etc. Modern agriculture recognizes the effect 

 of germ life in the various processes of fertilization by natural 

 manures; in the accumulation of nitrogenous food in the soil 

 as a result of the action of nitrification, and in the fixation of 

 free nitrogen of the air by members of the clover family. 



Sometimes the bacteria are to us a scourge, but often, in- 

 deed, they come in the character of a friend and helper. 

 More especially is this true of that class that are associated 

 with dairy products, for in both the butter and cheese indus- 

 tries, success is only assured through the activities of certain 

 favorable forms. 



The following pages attempt to show this group of organ- 

 isms so infinitely small yet almost infinitely powerful in 

 their relation to the dairy and dairy products. 



Knowledge in dairying, like all other technical industries 

 has grown mainly out of experience. The facts have been 

 learned by observation, but the why of each is frequently 

 shrouded in mystery. 



