I ix.j I^ejlr. 95 



or almost all, occasions on which lactic acid makes its appear- 

 ance in considerable quantities we may expect to find a ferment- 

 organism, and indeed a Bacterium which produces it, but this 

 need not always be the one form, described above as that of 

 ordinary acidification of milk. It is well to call particular 

 attention to this point on account of the wide diffusion of lactic 

 acid, for example in human food, whether this be purposely 

 made sour, as in ' sauerkraut ' and the like, or is a case in which 

 the turning sour indicates decomposition, as in soured vegetables 

 or beer, so far as the effect in the latter case is not due to the 

 presence of acetic acid. 



6. This will be the best place to recur briefly to the Bac- 

 terium of kefir mentioned above on page 13, which is connected 

 with an interesting change in milk. It was discovered by E. Kern 

 in 1883 (46). Kefir or kephir is the name of a drink, a fluid 

 eff'ervescing kind of sour milk containing a, certain amount of 

 alcohol, which the inhabitants of the upper Caucasus prepare 

 from the milk of cows, goats, or sheep, and therefore not to be 

 confounded with the koumiss obtained by the Nomads of the 

 Steppe originally from mares' milk, with which we are not at 

 present concerned. The drink is prepared by adding to the' 

 milk the bodies described above as a beautiful example of 

 Zoogloeae, which bear the name of kefir-grains. The Cauca- 

 sians make use in this process of leathern bottles to hold the 

 milk, the more polished European employs less objectionable 

 glass vessels. The recipe followed by the latter is mainly as follows. 



Living and thoroughly moistened kefir-grains are added to 

 fresh milk in the proportion of i volume of the grains to about 

 6-7 volumes of milk. The mixture is exposed to the air for 

 twenty-four hours at the ordinary temperature of a room, pro- 

 tected from dust by a loose covering only, and is frequently 

 shaken. At the end of twenty-four hours the milk is poured 

 off from the grains, which may be employed again for a fresh 

 preparation. The milk itself, which we will term ferment-milk, 

 is then mixed with twice the quantity of fresh milk, put into 



