365 
This, however, is at once neutralized by the ammonia present, and 
exists in the liquid in the form of ammonium butyrate. 
Alcoholic fermentation of milk . — Among the abnormal fermenta- 
tions of milk may be mentioned the alcoholic fermentation, which is 
accomplished by certain yeasts, aided in their action by certain 
species of bacteria. While alcoholic fermentation of milk is abnormal 
in the sense that it never occurs in milk spontaneously, but must be 
induced by direct inoculation with certain ferments, it is employed in 
the production of certain milk beverages, such as koumiss and kefir, 
6tc., which in certain countries are highly esteemed as articles of 
diet, and have in recent years come into more of less general use as 
food for invalids, etc. Koumiss, originally made by the alcoholic 
fermentation of mare’s milk, is now made from cow’s milk by the 
addition of cane sugar and yeast. The first action of the ferments is 
to hydrolyse the polysaccharides (cane sugar and lactose) producing 
the simpler sugars, glucose, levulose, and galactose, all of which are 
fermentable by yeast. Two changes then occur, the alcoholic fer- 
mentation, resulting in the production of alcohol and carbon dioxide, 
and the ordinary lactic acid fermentation, resulting in the produc- 
tion of lactic acid. Kefir, a similar beverage, originating in the 
Caucasus, is also made from milk by an alcoholic fermentation. The 
fermentation is carried out in leather bottles, and is started by means 
of u kefir grains,” concerning whose origin but little is known. Dur- 
ing the fermentation thus induced a considerable quantity of the 
ferment is produced, which is removed and dried in the sun, and thus 
new supplies of the kefir grains obtained. Struve (32) gives the fol- 
lowing proximate chemical analysis of kefir grains dried at 100° C. : 
Per cent. 
Water 11. 21 
Fat 3.99 
Soluble peptone-like substances 10. 98 
Proteids soluble in ammonia 10. 32 
Proteids soluble in caustic potash 30. 39 
Insoluble residue 33. 11 
100. 00 
The whole of the active matter of the ferment was contained in 
the insoluble residue. A microscopic examination of this showed it 
to consist of a mixture of yeast cells with Bacterium dispora Caucasica 
(Kern). In a few specimens leptothrix and oidium lactis were also 
present. According to this author, the yeast cells, which have been 
somewhat modified by* their growth in leather bottles, are alone 
responsible for the peculiar kefir fermentation. 
According to Yieth (33) milk sugar ordinarily does not readily 
undergo alcoholic fermentation with yeast. With kefir grains, how- 
