BACTERIA IN SEPARATED MILK 147 



bowl sediment will contain the majority of the organisms con- 

 tained in the whole milk, pathogenic or non-pathogenic, the next 

 largest amount of organisms will be in the separated milk, and 

 the smallest quantity, pathogenic or otherwise, in the separated 

 cream. Roughly, 60 per cent, of the organisms will be found in 

 the bowl sediment, 25 per cent, in the separated milk, and 15 per 

 cent, in the separated cream.^ The matter is important, as it is 

 claimed by certain makers or vendors of separators that mechanical 

 separation " filters " milk of its organisms, and removes, in particular, 

 its pathogenic bacteria. To a certain extent this is undoubtedly 

 true. But it must be remembered that only about half are 

 removed. 



In 1899, in order to test the effect of centrifugalisation upon 

 pathogenic organisms in milk, we carried out a series of experiments 

 with the B. tuberculosis, as follows : — Some 5 or 6 gallons of ordinary 

 fresh country milk was taken, and to it was added a pint of human 

 tuberculous sputum, which was thoroughly disintegrated in water 

 and mixed with it. The whole was then poured into the pan of 

 a Lister's " Alexandra " separator. From the pan the milk passed 

 in the ordinary way into the bowl of the separator, which had been 

 sterilised, and was separated. On examination of the slime, the 

 separated milk, and the separated cream, the tubercle bacillus was 

 chiefly found in the slime, but was also present in the milk and 

 cream. Subsequently, butter and cheese (" skim-milk " cheese) 

 were made from the cream and milk respectively, and in both 

 butter and cheese the tubercle bacillus was readily found. Hence 

 it may be taken as a fact that when milk contains the tubercle 

 bacillus, all its products — cream, butter, cheese, whey — may also 

 contain it. 



Moore - conducted a number of experiments to determine the 

 effect of the separator in removing certain pathogenic germs, and 

 found that although considerable numbers are removed with the 

 slime, some remained in the separated milk and cream. His 

 results and those of several European investigators are in accord- 

 ance with our own. 



Species of bacteria present in milk. — Probably the most con- 



^ As a result of some recent experiments, Eckles and Barnes have estimated 

 that only 47 per cent, of the organisms appear in the shme, 29 per cent, in the 

 separated milk, and 24 per cent, in the cream. They hold that separation removes 

 36 per cent, of the organisms from the milk and cream. {Iowa Sta. Bulletin^ 

 1902, lix., 55-59.) 



2 United States Department of Agriculture Year Book ^ 1895, p. 439. 



