371 
According to Trillat and Sauton (32), bitter milk contains alde- 
hydes and ammonia, and results from the simultaneous inoculation 
of fresh milk with a yeast producing aldehydes, and an ammonia- 
forming bacillus, B. Flligge, V. 
' The alkaline fermentation of milk . — It has been observed that 
boiled milk never turns sour by spontaneous fermentation. On the 
other hand, when boiled milk is allowed to stand at ordinary tem- 
peratures it gradually acquires an alkaline reaction, ofttimes a bit- 
ter taste, and finally curdles, yielding a soft, slimy curd. On further 
standing this curd gradually dissolves to form a somewhat clear 
liquid, and if the fermentation be allowed to proceed for a sufficient 
length of time a semitransparent liquid is obtained, having no resem- 
blance to milk. As with the other fermentations of milk, a number 
of organisms are capable of causing the alkaline fermentation of milk, 
and a considerable number of substances are produced as the result 
of these changes. Among the substances found in milk which has 
undergone the alkaline fermentation may be mentioned the peptones, 
which are believed to be responsible for the bitter taste, leucin, tyrosin, 
and ammonia, which latter imparts to the liquid the characteristic 
alkaline reaction. Butyric acid is also formed in this fermentation. 
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. lYhile the alcoholic fermentation of milk is ab- 
normal 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 kou- 
miss and kefir, etc., which in certain countries are highly esteemed as 
articles of diet, and have in recent years come into more or less gen- 
eral 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 Koumiss, originally made by the 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 fer- 
ments is to hydrolyze 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 alco- 
holic fermentation, resulting in the production of alcohol and carbon 
dioxide, and the ordinary lactic acid fermentation, resulting in the 
production 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 “ kefir grains,” concerning whose origin but little is known. 
During the fermentation thus induced a considerable quantity of the 
ferment is produced, which is removed and dried in the sun, and thus 
