INTRODUCTION 



The purpose of the course here outlined is to train the 

 student in those bacteriological processes that are necessary 

 for him to comprehend thoroughly, before he is in a position 

 to appreciate the relation of microorganisms to dairy processes. 

 This work is of fundamental importance to the student who 

 wishes to learn the nature of the biological changes going on 

 in milk and its products, whether he is concerned purely with 

 the practical side of dairying or is interested in the cognate 

 work of dairy chemistry or dairy bacteriology. 



The attempt has been made to keep the scope of this work 

 within the realm of dairy bacteriology, and not encroach upon 

 the field of dairy manufactures. For example, in the study of 

 starters it is desirable that the bacteriological student should 

 know how to determine the purity and vigor of a culture, but 

 the practical propagation of the starter should be presented 

 from the creamery point of view. The effect of the ripening 

 of cream on the churning process and the action of acid on the 

 physical condition of cheese are instances of biologic activity 

 that can better be studied in the factory than in the labora- 

 tory. In many cases it would be advantageous if the practi- 

 cal and theoretical work could be carried on simultaneously. 

 Thus, in studying a starter bacteriologically it would be very 

 desirable to test in the laboratory by frequent examinations 

 the purity of the starter as it is handled in the dairy from 

 day to day. The possibility of deterioration could then be 

 ascertained from both the practical and scientific points of 



iii 



190829 



