CHAPTER XXXVI. 



THE BACTERIOLOGY OF MILK IN ITS RELATION TO DISEASE. 



FROM the standpoint of the dairy and cheese producer a study of the 

 different varieties of bacteria of the air and dust are of importance. 

 Some yield products which give the butter, cheese, milk, or cream 

 a bad taste or odor. We can only consider here the bacteriology of 

 milk so far as it is related to health and disease. 



The bacteria in milk can be divided into two great groups those 

 which get into the milk after it leaves the udder and those which 

 come from the cow. The first group comprises bacteria from dust, etc. 



The extraneous bacteria are of importance because they produce 

 changes in the chemical composition of the milk when they have devel- 

 oped in great numbers. The number of bacteria in any sample of 

 milk depends on three factors : the number deposited in the milk from 

 the cow's udder, from the air, and utensils ; the time during which they 

 have developed, and the temperature at which the milk has stood. 

 The last is perhaps the most important. The attempt was made dur- 

 ing the past three years to connect illness in children with the varieties 

 of bacteria in milk. As a matter of fact no such connection was made 

 out. The number of varieties was found to be so great that if any 

 special type of disease had developed in those getting milk it would 

 have been an extremely difficult thing to have made out such a connec- 

 tion. 1 This in spite of the fact that the varieties isolated represent only 

 the species present in greatest number in the milk examined, for in no 

 case was more than 0.01 c.c. of a milk, and in most highly contaminated 

 milks only 0.001 c.c., used in making a plate, and varieties which 

 occurred in too small numbers to be present in this quantity would 

 necessarily be missed. For the purposes of this book it is not con- 

 sidered desirable to burden the reader with the enumeration of the 

 varieties of bacteria found in the different samples of milk and their 

 characteristics. Only a brief summary of the results will be given. 



1 The bacteria were isolated from the milk through plating in a 2 per cent, lactose-litmus nutrient 

 gelatin or agar, and later grown upon the usual identification media. The pathogenic properties of 

 the different bacteria were tested by intraperitoneal and subcutaneous inoculation in guinea-pigs 

 with 2 c.c. of a forty-eight-hour broth culture, and by feeding young kittens for several days with 

 3 to 6 c.c. daily of a twenty-four-hour broth culture by means of a medicine dropper. 



With the characteristics of the bacteria thus determined, they were then separated into classes 

 following as nearly as possible the lines suggested in Chester's Manual of Determinative Bacteri- 

 ology. Further attempt was then made to identify as many as possible of the varieties with those 

 previously described, using the descriptions of Chester and Migula. With a great many this proved 

 unsatisfactory or impossible because cf the incomplete descriptions in literature, or the lack of all 

 description. 



