76 EXPERIMENT STATION EECOItD. IVol. 38 



tinder sanitary conditions of a grade equal to that required for certified milk. 

 Tests were made on tlie effect of the clarifying process on the number of 

 bacteria, the subsequent activity of the organisms, and the keeping quality of 

 the milk. On 15 tests the milk before clarification contained from 2,600 to 

 5,500 with an average of 3,640 bacteria per cubic centimeter, while the milk 

 after the process contained from 4,900 to 10,900, with an average of 7,027 bac- 

 teria per cubic centimeter. " The increase in the number of bacteria in the 

 clarified milk is, of course, only an apparent one and is due to the agitation of 

 the machine which breaks up the clumps of bacteria, thus increasing the 

 count as determined by the plate culture method." 



Reduction tests were made in order to test the relative physiological activities 

 of the microorganisms in ordinary and clarified milks. The tests were made 

 by adding 10 cc. of milk with 1 cc. of a solution of 1 gm. methylene blue to 2 

 liters of physiological salt solution, and incubating at 37° C. For the deter- 

 mination of the reducing powers of the milks, five check samples each were 

 run on the clarified and unclarlfied milks in each test. Four such tests were 

 run, and in every case the reduction took place sooner in the clarified milk. 

 The differences were well marked jmd indicated that the clarifying process 

 actually stimulates the activity of the organisms contained in milk. 



A study of the keeping quality of milk as affected by clarification showed 

 that in each of the four samples tested the development of acid in milk held 

 at 10° was greater in clarified than in normal milk. In these tests the clarify- 

 ing process did not appear to have any hygienic significance, as evidenced by 

 its failure to remove streptococci to a measurable extent. 



II. The sistniflcance of the udder flora in the production of high-grade milk. — 

 In the course of other work it has been noticed that relatively large numbers 

 of bacteria occur in the udders of certain cows, and that the existence of such 

 animals is more frequent than is ordinarily thought. Of 142 cows, from six 

 different herds which have been examined, 19 have been found to give over 

 10,000 bacteria per cubic centimeter in their fresh milks, while in 41 cows the 

 number of organisms exceeded 5,000 per cubic centimeter. Two of the animals 

 mentioned gave milk containing over 100,000 bacteria per cubic centimeter. All 

 of the cows were in normal healthy condition. 



In order to show the relation of the udder flora to the bacterial content 

 of the finished product, 12 cows of the college herd were selected, 6 of which 

 had low numbers of microorganisms in their udders, while the other 6 har- 

 bored relatively large numbers. Three tests were made at intervals of several 

 days of the milks from all 12 of the individual animals. The average bacterial 

 count of the 6 low-group cows was 140 and of the 6 high-group cows 10,590 

 per cubic centimeter. 



The milks from these two groups of cows were also collected separately for 

 a period of 15 days. The milks from the animals of the low group were placed 

 in one can and those from the animals of the high group in another can. All 

 of the cows were milked by two men, each milker taking three cows from each 

 of the two groups. The milking was done with no extra precautions, the milks 

 then being weighed, strained, cooled, etc, in the usual way. Samples were 

 taken after the milk had been exposed to all the handling it gets up to the 

 bottler. The averages of the counts for the 15 days were 411 for the morning 

 milk and 296 for the evening milk of the cows of the low group, and 11,240 for 

 the morning milk and 7,353 for lie ffeening mHk of the cows of the high 

 group. 



III. The normal occurrence of streptococci in wtTk.— During the past year 

 examinations for streptococci have been made of the milks from the individum 



