240 BACTERIA IN MILK AND MILK PRODUCTS 



cells, bacteria, etc. The milkers are under strict medical supervision, and regula- 

 tions are enforced in respect of " cleanliness." Cows are milked in their own stalls, 

 but immediately after milking the milk is taken in closely-covered vessels to the 

 milk-room, where it is cooled and screened. The milk-room is a specially prepared 

 chamber, having smooth surfaces of polished cement, and specially constructed 

 ventilators with cold-water sprays to moisten the air and prevent dust gaining 

 access, asepsis being the requirement. The milk is now ready for the laboratory. 

 (6) Modification. The object of the Walker-Gordon Laboratories is first to insure 

 and distribute the naturally pure milk ; and secondly, to provide a place where 

 different combinations of milk may be put up, according to the prescriptions of 

 medical men, with accuracy, and under such conditions of cleanliness and asepsis as 

 to insure the best possible food for infant feeding. The necessity for modification 

 arises from two facts, namely, that milk varies in constituent percentages, and to 

 obtain a regular and uniform constitution, modification is necessary ; and secondly, 

 some children require, for one reason or another, a milk containing certain per- 

 centages of the various constituents. Thus the patient can receive on the physician's 

 order a mixture of the percentages called for, made up of either separated cream or 

 gravity cream, separated milk or whole milk. Twelve years' experience in Boston, 

 U.S.A., seem to indicate the practicability of this system in preventing the summer 

 diarrhoea of infants due to contaminated milk. 



In addition to these two types, there are various similar methods in vogue, each 

 of which has its points of advantage.* 



BACTERIA IN MILK PKODUCTS 



Cream is generally richer in bacteria than milk. Set cream 

 contains more bacteria than separated cream, but germs are abundant 

 in both. The number of organisms found in cream is enormous. 

 Probably no other natural medium contains more. We have 

 frequently examined fresh cream in the country, and found it to 

 contain more than 100,000,000 bacteria per c.c. It is not only a 

 favourable medium. It is the filter, so to speak, of milk. For, as 

 the cream rises, the milk parts with more than 90 per cent, of its 

 contained bacteria. Conn and Estenf found 110,000,000 of bacteria 

 per c.c. in unripened cream (average of four examinations) and 

 284,000,000 in the same cream ripened (average of four examinations). 

 Cream obtained from a creamery gave an average on eight examina- 

 tions of 56,000,000 organisms per c.c. unripened, and 350,000,000 

 organisms per c.c. ripened. Other examples of unripened cream 

 averaged more than 90,000,000, but when ripened averaged over 

 300,000,000. Normally ripened cream probably averages four or 

 five hundred millions of bacteria per c.c., which is greatly in excess 

 of any other natural media. The number of organisms in unripened 

 cream varies widely. 



The most characteristic feature of cream-ripening is the growth of 

 the acid-producing organisms, chiefly B. acidi lactici, and the decline 

 of the liquefying and extraneous organisms. B. acidi lactici is found 

 in very small numbers in fresh milk, as we have already pointed out, 



* For full account, see Jour, of Hygiene, 1904, p. 329 (McCleary). 

 t Thirteenth Annual Report of the Storr's Agricultural Expt. Sta., Connecticut, 

 1900, pp. 13-33. 



