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caused by the lactobacillus. Methods for isolating these organisms 
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. 
Reference has already been made to the fact that the lactic acid 
fermentation of milk is used commercially in the manufacture of 
lactic acid. The lactic acid fermentation of milk is also turned to 
practical account in the manufacture of cheese. It lias been shown 
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- 
mentation and also with regard to the peculiar kind of cheese desired. 
Similar views regarding the ripening of cheese are held by Von 
Freudenreich (23). According to this author the lactic acid bacteria 
play the preponderating if not the exclusive role in the ripening of 
Emmenthaler cheese. Similarly Boekhaut and de Vries (24) have 
shown that cheese which does not contain the lactic acid bacteria 
does not ripen. On the other hand Chodat and Hofman-Bang (24a) 
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 (25) 
found that when only rennet is allowed to act on milk no cheese 
flavor is developed. 
Abnormal fermentations of milk . — Under ordinary circumstances 
milk usually undergoes the lactic acid fermentation. It turns sour 
and curdles and the production of lactic acid puts a stop, tempora- 
rily at least, to all other bacterial changes. Hence in normal milk 
it is only rarely that fermentation other than souring occurs. Under 
certain conditions, however, the milk becomes infected with a great 
variety of micro-organisms and various changes in its composition 
are brought about. By some authorities these have been called 
abnormal fermentations. As a result of these fermentations, altera- 
tions take place in the color, odor, and taste of the milk, and in some 
instances highly poisonous substances are produced. In this con- 
nection Burri and Dueggeli (26) have recently had occasion to exam- 
ine four samples of milk in which such alterations had occurred. 
According to these authors sample (1) had the peculiar^ disagree- 
able odor of Limburger cheese, sample (2) the odor of dogs, sample 
(3) a bitter taste, and sample (4) the odor and taste of Schabzieger 
