DAIEY FARMING DAIRYING. 75 



tin. Various types of tliis group are able to survive pasteurization and vary 

 widely in tlieir cultural characteristics. 



" Tlie few gas-forming bacteria in pasteurized milk, so far as the results of 

 this investigation indicate, do not include organisms of the colon-aerogenes 

 group. One gas-forming organism was found which produced gas in milk and 

 peptonized casein. Another culture, known as Z, seems to be an entirely new- 

 type, which is characterized by its ability to produce gas continuously in milk 

 through a long period, and by the fact that while gas is formed in milk none is 

 formed in lactose broth. 



" Gas-forming anaerobic bacteria are often found in milk which produce gas 

 in lactose bile tubes and which might be mistaken in a preliminary test for the 

 colon organism. In view of this fact, it seems advisable to suggest that boards 

 of health which depend on the presence of the colou-aerogeues group as an 

 indication of reinfection or inefficient pasteurization make a complete determina- 

 tion by cultural reactions of organisms suspected as being colon forms. 



"The thermal death point of one lactic acid organism isolated during this 

 investigation was 79.4° C. (175° F.) when a broth culture was heated in Stern- 

 berg bulbs for 30 minutes. The thermal death points of 64 acid-forming bac- 

 teria from one sample of milk which survived pasteurization for 30 minutes at 

 82.2° C. determined roughly was between 82.2° C. and 93.3° C. (200° F.). 



" Only a small percentage of spore-forming bacteria are found in milk pas- 

 teurized for 30 minutes at 62.8° C. Of 225 cultures selected at random which 

 were studied, only 3, or 1.35 per cent, formed spores. 



" For those who advocate the inoculation of pasteurized milk, after heating, 

 with a culture of lactic acid bacteria to produce a normal souring, it is sug- 

 gested that a culture of a high-temperature resisting lactic-acid organism may 

 be added before pasteurization. By such a method there would be no danger 

 of infection as might result accidentally by inoculation after pasteurization. 



" In view of the results of this investigation it seems that the control of pas- 

 teurization should be maintained by bacterial limits for the milk to be pasteur- 

 ized, together with supervision which will insure the use of the proper 

 pasteurizing temperature and guard against reinfection. A bacterial standard 

 then need not be set for pasteurized milk." 



A comparison of the acid test and the rennet test for determining the con- 

 dition of milk for the Cheddar type of cheese, E. G. Hastings and Auce C. 

 Evans (U. 8. Dept. Agr., Bur. Anim. Indus. Giro. 210, pp. 6). — In order to 

 determine the error in testing the acidity of milk by the til ration method, 

 known quantities of acid were added to milk and the average error was found 

 to be 0.01 per cent, even when 50 cc. of milk was titrated. With a less ex- 

 perienced operator, working under conditions that exist in cheese factories, 

 the error would be at least twice this amount, as was determined by actual trial. 



That the bacterial content of milk can not be determined by the acidiry was 

 shown by the following test : A sample of milk having an acidity of 0.17 per 

 cent was divided into 2 portions. To one portion rennet was added; (he second 

 was kept at 86° F. for 1 hour. At the end of this period the acidity was still 

 0.17 per cent, but the bacterial content must have been several times greater 

 than in the first sample. 



As an illustration of the superior sensitiveness of the rennet test, one sample 

 was curdled in 3 minutes 30 seconds with rennet, while milk originally from 

 the same sample, after incubating for 4 hours 45 minutes, was curdled by 

 rennet in 1 minute 30 seconds. The difference in the acidity of the 2 milks, 

 however, was only 0.018 per cent, the difference being within the limits of eri'or 

 of titration. The rennet test closely paralleled the change in bacterial content. 



