THE BACTERIA FOUND IN MILK 35 



The comparative value of these tests, with an analysis of the 

 results obtained with them by MacConkey and by Orr, is 

 discussed in Chapter X. 



The chief value of the B. coli group in milk is that it, 

 as a group, indicates the addition to milk of manurial or other 

 undesirable pollution. The members of this group are, in 

 the first place, extremely abundant in the excreta of both 

 man and animals. They are absent, or almost absent, from 

 the milk of individual cows, or from milk collected under 

 conditions of great care and cleanliness. This fact has been 

 demonstrated by a number of workers. 



For example, Harrison 1 examined the milk of 25 cows, 

 the milk being collected direct into sterile vessels, and after 

 the udders and flanks had been wiped with a damp cloth 

 and the first milk rejected. From only two of the cows were 

 gas-producing bacteria isolated. 



Von Freudenreich examined 15 samples of milk taken 

 direct from the udder, and found no B. coli or other glucose 

 fermenters in any of the samples. 



The writer 2 found glucose-fermenting organisms in 4 out 

 of 52 samples of milk from the mixed four quarters of in- 

 dividual cows. In one of these, the examination of the separate 

 quarters a few days previously had shown the presence of B. 

 coli in three out of the four quarters. In the collection of the 

 samples strict aseptic precautions were not taken, so probably 

 some of the glucose fermenters were from outside contamination. 



MacConkey 3 records that in samples drawn direct from 

 the cow no gas-forming organisms were met with. 



The presence of lactose-fermenting organisms of coli type 

 in fresh milk is also largely proportional to the amount of 

 cleanliness exercised in milking. This is illustrated by the 

 following table, 4 in which comparison is instituted between 

 the general cleanliness classification at the cowshed (made 

 before the bacteriological examination was started) and the 

 number of bacteria, and number of B. coli and allied organisms. 

 All the milk samples were collected at the farm and examined 

 without delay. 



1 CentralU.f. BakL, 1905, Abt. II. xiv. 359. 

 2 Report of Medical Officer, Local Government Board, 1906-7, p. 205. 



3 Journ. of Hygiene, 1906, vi. 385. 

 4 Savage, Report of Medical Officer, Local Government Board, 1909-10, p. 480. 



