EXPERIMENT STATION BULLETINS. 533 



that in summer a large percentage of the samples of cream analyzed 

 contained as many as 100,000 gas producing bacteria per cubic centi- 

 meter. By inoculating pasteurized cream with gas producing bacteria, 

 Harrison (7, p. 7) observes that the butter had a bitter, disagreeable 

 and astringent flavor and concludes that these organisms are as injuri- 

 ous to the flavor of butter as they are to the flavor of cheese. The group 

 of anaerobic sporebearing gas producers (B. enteriticUs sporof/enes,) 

 or B. welchii) which are interesting because they sometimes cause intesti- 

 nal disturbances and are indicators of manurial pollution, are found to 

 be present in small numbers in milk and cream, but from the work of 

 Kosenau, Frost and Bryant (13) , enter itidls spores are not found in butter 

 although their presence in the cream was demonstrated. Liquefying bac- 

 teria which are numerous in soil and on feeds (3) find their way in large 

 numbers into milk (15, p. 18) and from thence to cream (9, pp. 10 and 

 11). Ayers and Johnson (1, p. 59) find that the relative proportion of 

 the groups of peptonizing and lactic acid bacteria is approximately the 

 same in efficiency pasteurized milk as it is in clean raw milk ; the percent- 

 age of liquefiers (1, pp. 79-82 and 90-92) range about 5 to 25 per cent, and 

 of the acid producers about 30 to 70 per cent of the total flora. For con- 

 tinuous pasteurization of cream a temperature between 74° C. and 80° 

 C. is recommended bj^ Rogers, Berg and Davis (11, pp. 310 and 32G) who 

 show that from 99.7 per cent to 99.9 percent of the total flora is killed. 

 Also they conclude from their results that the catalase and the lipase in 

 milk are destroyed at 70° C, peroxidase at 77° C, and that galactase is 

 not destroyed at 93° C. Data given by Rogers, Berg, Potteiger and 

 Davis (12, p. 33) show the number of bacteria in cream from a skim- 

 ming station to be approximateh^ 50,000,000 per cubic centimeter which 

 they group as acid formers about 26.5 percent, as alkali formers about 

 4 percent, as peptonizers about 6.5 percent and as inert about 53 

 percent. The total number of microorgaisms in sour cream as 

 it arrived at the creamery was found by Hammer (5, pp. 37-40) 

 to be in the hundred millions; and pasteurization at 63° C. for 20 minutes 

 and at 83° C. by the flash method gives approximately the same results, 

 i. e., 99.99 percent efficiency. As a result of a series of analyses by Sayer, 

 Rahn, and Farrand (14, pp. 28-45) various types of microorganisms are 

 found in butter; Bad. lactis acicU was omnipresent, a small irregular 

 yeast was present in most samples and Micrococcus lactis varians, an 

 organism present in many udders, was found frequently. Rahn, Brown 

 and Smith (10, pp. 35-40) gives data showing that liquefying and non- 

 liquefying torulae and Oospora lactis {Oidium) are present in butter 

 frequenth^ and sometimes in rather large numbers. 



While the literature cited on this subject is by no means exhaustive 

 and while it is admitted that other data fully as conclusive have not been 

 mentioned, yet it is believed that this review will serve amply as an in- 

 troduction to the subject. 



