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I Quite recently Beyerinck (21) has again discussed the lactic fer- 
I mentation of milk. He has found that temperature and oxygen 
i| pressure determine the nature of the autofermentation of milk. At 
' temperatures below 40° C. the fermentation brought about by B. 
l! coli is replaced by a butyric acid fermentation, which, after lasting 
I ! some time, is succeeded by a lactic acid fermentation. In good milk, 
!j even at 40° C., at which temperature gas-producing bacteria develop 
i most rapidly, no gas is produced. This fact therefore forms the 
!| basis of a dairy test for judging of the purity of milk. He recog- 
1, nizes three forms of lactic acid fermentation depending on the tem- 
j ! perature. At very low temperatures there occurs the slimy lactic acid 
|! fermentation, which, according to this author, is due to the smaller 
: cell Avails of the organism. At medium temperatures the common 
! lactic acid fermentation predominates, this being caused by the lacto- 
I coccus and at higher temperatures the lactic acid fermentation 
! caused by the lactobacillus. Methods for isolating these organisms 
I from milk are given, and also their morphological characteristics 
; and their zymotic reactions. He, like other observers, has found the 
lactic acid ferment to be very variable. 
Keference has already been made to the fact that the lactic acid 
fermentation of milk is used commercially in the manufacture of 
. . . . j* ^ . 
! lactic acid. The lactic acid fermentation of milk is also turned to 
practical account in the manufacture of cheese. It has been shown 
I by Epstein (22) that the ripening of cheese is due largely to the 
action of organisms which induce the lactic acid fermentation. 
Each particular kind of cheese is produced by the agency of special 
organisms which act chemically by means of enzymes and give rise 
to the peculiar odor and flavor of the cheese. These organisms are 
chosen both with regard to their power to induce the lactic acid fer- 
I mentation and also with regard to the peculiar kind of cheese desired. 
I Similar views regarding the ripening of cheese are held by Von 
I Freudenreich (23). According to this author the lactic acid bacteria 
I play the preponderating if not the exclusive role in the ripening of 
I Emmen thaler cheese. Similarly Boekhaut and de Vries (24) have 
I shown that cheese which does not contain the lactic acid bacteria 
I does not ripen. On the other hand Chodat and Hofman-Bang (25) 
are of the opinion that the importance of the lactic acid bacteria in 
the ripening of cheese has been overestimated, and attribute the 
greater number of the changes occurring in this process to another 
organism — namely, tyrothrix. 
In this connection it is interesting to note that Van Slyke (26) 
found that when only rennet is allowed to act on milk no cheese 
flavor is developed. 
