DAIEY FAEMING DAIRYING. 277 



milk — are held, the group relations change; but if the changes which take 

 place are compared it will be found that they are the same in each. At the 

 time of souring, the group proportions have changed so that the lactic-acid 

 bacteria constitute the largest group with the alkali or inert forms next in 

 order and the pept^"Izers in the smallest proportion as initially. In both of 

 these milks the group of peptonizers may increase slightly in its proportion 

 to the other two groups during the first two days, but it then gradually de- 

 creases and always forms the smallest group. 



" When milk is less efficiently pasteurized the position of the groups may be 

 reversed so that the lactic-acid bacteria constitute the largest group with the 

 alkali or inert forms next in order, but here again the peptonizers form the 

 smallest proportion of the total bacteria. This group arrangement is the same 

 in a dirty raw milk. 



" The more efficient the pasteurization, the smaller the percentage of lactic- 

 acid bacteria ; and, similarly, the cleaner the raw milk, the smaller the per- 

 centage of lactic-acid bacteria. 



" The peptonizing bacteria are present in smaller numbers in the inferior 

 grades of commercially pasteurized milk during the first twenty-four hours 

 after receiving than in raw milk of the same quality, and the peptonizers may 

 increase to slightly higher numbers in the pasteurized milk when held several 

 days than in the raw milk of high initial lactic-acid bacteria content; but it 

 should be x'emembered in this connection that milk is usually consumed within 

 twenty-fours hours after delivery. The number of peptonizers in a good grade 

 of commercial pasteurized milk on the initial count and on succeeding days is 

 approximately the same as in a clean raw milk when held under similar 

 temperature conditions. 



"All milk, whether pasteurized or raw, must necessarily be infected during 

 cooling and bottling by bacteria in the receiving tanks, in the pipes, on the 

 cooler, and in the bottles; but the low bacterial counts obtained from pasteur- 

 ized milk in these investigations show that the reinfection must have been very 

 small. . . . 



"The 'holder' process of pasteurization is superior to the 'flash' process. 

 With the ' holder ' process a high efficiency may be obtained with a low tempei'a- 

 ture, while to obtain the same efficiency with the ' flash ' process a high tempera- 

 ture would be required. A temperature of 62.8° C. (145° F.) for 30 minutes 

 seems best adapted for efficient pasteurization. . . . 



" Pasteurization should always be under the control of competent men who 

 understand the scientific side of the problem. It is believed that ignorance of 

 fundamental bacteriological facts often accounts for inefficient results rather 

 than a willful lack of care on the part of the dairyman." 



The daily variation in the bacterial content of raw and pasteurized milks 

 during the incubation period is presented in tabular form. References to the 

 literature on the subject are appended. 



The bacteriolog-y of soured milk, R. T. Hewlett (JBrit. Med. Jour., 1910, 

 No. 260S, pp. 158Ji-l586). — This article is concerned with the methods of prepa- 

 ration and administration of soured milk in lactic-acid therapy. 



The fermentation of citric acid in milk, A. W. Bosworth and M. J. Prucha 

 {New York State Sta. Tech. Bui. IJf, pp. J,3-48).—A study of the disappearance 

 of citric acid in sour milk. 



Milk containing 0.224 gm. citric acid was found to be free from the acid in 

 60 hours. In order to determine whether the citric acid could be fermented 

 under conditions other than those present in milk, 5 gm. of calcium citrate were 

 placed in 4 fiasks containing 500 cc. of bouillon and 1 per cent of lactose. After 

 sterilizing, 2 flasks were kept for checks and into each of the other 2 flasks 1 cc. 



