CHAPTEE XIV 



INTERPRETATION OF RESULTS AND BACTERIOLOGICAL STANDARDS 



FOE MILK 



Milk is liable to bacterial pollution from numerous sources, 

 but they can all be included into three groups : 



A. Bacterial contamination from the cow herself before 

 the milk leaves the teats. This may be with harmful bacteria, 

 such as the tubercle bacillus or some streptococci ; or harmless, 

 such as from saprophytic streptococci and staphylococci present 

 in the milk cistern of the udder. 



B. Bacterial contamination from specific disease-producing 

 bacilli, such as B. typhosus or B. diphtheriae, gaining access to 

 the milk from infected sources. 



C. General bacterial contamination due to insufficient 

 cleanliness at the time of milking and subsequently up to the 

 time of consumption. 



The first two sources are very different from the third, 

 and involve the detection of certain special disease-producing 

 bacilli. -For these the actual detection is all that matters, and 

 their quantitative presence is comparatively immaterial. With 

 infection from these two sources there is no question of 

 numerical standards, and difficulties in the interpretation of 

 results do not arise. The third source of pollution is very 

 different, and the quantitative estimation of bacteria, or groups 

 of bacteria, is of essential importance. This necessitates the 

 consideration of the question of standards and the interpretation 

 of results. 



To measure the general bacterial contamination of milk 

 the following procedures are available : 



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