BACTERIA IN THE INDUSTRIES 193 



supplied provided sanitary rules and regulations are strictly observed and 

 enforced. 



Temperature and climatic conditions are of great importance in 

 regulating the bacterial contamination of milks. Thus there is in many 

 states and localities, a summer standard and a winter standard. Again, 

 the varied and variable dairying conditions has resulted in the recognition 

 of several grades of milk, as certified, guaranteed, Grade A, Grade B, etc. 



The milk from diseased animals is universally recognized as objec- 

 tionable and no one would knowingly use such milk. Milk also serves as a 

 carrier of disease, such as tuberculosis, various forms of coccic and strepto- 

 coccic infection, typhoid, dysentery, diphtheria, etc. These are aU matters 

 of general knowledge to sanitarians and need not be discussed more fully. 



2. Milk Impurities. Under the compound microscope, ordinary cow's 

 milk may show the following elements. 



a. Butter fat globules. Variable in size, occurring singly and more or 

 less agglutinated. 1 



b. Casein granules. Very minute and formless, granular. 



c. Body cells. Epithelial cells, leucocytes, red blood corpuscles, pus 

 corpuscles. 



d. Impurities derived from cow, from cow stable, from cattle feed. 



e. Impurities derived from milkers. 



f. Impurities derived from containers. 



g. Impurities derived from air and dust. 



h. Pathologic impurities from the milk yielding animals and from the 

 human associates. 



As far as the micro-analytical examination of milk is concerned, no 

 attempt is made to identify the different species of microorganisms which 

 may be present. The essential is to determie whether or not the milk 

 in question is fresh, pure, and wholesome. 



3. General Milk Rating. Two distinct milk ratings must be noted. 

 The older rating based upon plate and tube cultures, still operative or 

 applied in most laboratories, and the more recent rating based upon direct 

 microscopical examination. The older method (plating method) gives 

 evidence of the approximate number of living bacteria present only and is 

 quite limited in scope and significance. The direct microscopical examina- 

 tion gives evidence as to the following. 



1. Total number of dead and living bacteria present. 



2. Body cells of all kinds. 



3. Colostrum (fat globules and characteristic ameboid body cells). 



4. Dirt and similar impurities present. 



5. Butter fat present. 



1 Boiling and pasteurizing causes the fat globules to agglutinate. 

 13 



