BACTERIA IN MILK 709 



cities, and the movement is daily gaining ground. Until fully estab- 

 lished, however, upon a financial basis which brings the best products 

 within the means of the poorer classes, other inexpensive measures to 

 render milk safe must often be resorted to. 



Sterilization by high temperatures is objected to by pediatricians 

 because of the physical and chemical changes produced in the milk 

 which are said to detract from its nutritive value. 



The development of scurvy and rickets in infants has often been 

 attributed to the use of such milk. These objections, however, do not 

 apply to the use of milk which has been subjected to the process of 

 "pasteurization." By this term is meant the heating of any substance 

 to 60 C. for twenty to thirty minutes. The process, first devised by 

 Pasteur for the purpose of destroying germs in wine and beer in which 

 excessive heating was supposed to injure flavor, brings about the death 

 of all microorganisms which do not form spores in other words, of all 

 the bacteria likely to be found in milk which can give rise to infection 

 per os. At the same time the chemical and physical constitution of the 

 milk is not appreciably changed, at least not to an extent which renders 

 it less valuable as a food. Statistics by Park and Holt * have shown 

 strikingly the advantages of pasteurized over raw milk in infant feed- 

 ing. Of fifty-one children fed with raw milk during the summer months, 

 thirty-three had diarrhea, two died, and only seventeen remained 

 entirely well. Of forty-one receiving pasteurized milk, but ten had 

 diarrhea, one died, and thirty-one remained entirely well throughout 

 the summer. The actual diminution of the living bacterial contents 

 of milk by pasteurization is enormous, the milk so treated often con- 

 taining not more than one thousand, usually less than fifteen thou- 

 sand, living bacteria to each cubic centimeter. 



Methods of Estimating the Number of Bacteria in Milk. In estimating 

 the number of bacteria in milk, colony counting in agar or gelatin plates 

 is resorted to. Great care must be exercised in obtaining the specimens. 

 If taken from a can, the contents of the can should be thoroughly mixed, 

 since the cream usually contains many more bacteria than the rest of 

 the milk. The specimen is then taken into a sterile test tube or flask. 

 If the milk is supplied in an ordinary milk bottle, this should be 

 thoroughly shaken before being opened, and the specimen for exam- 

 ination taken out with a sterile pipette. Dilutions of the specimen can 

 then be made in sterile broth or salt solution. If an initial dilution 



Park and HoU, loc. cit. 



