One of the organisms causing _Butyric Acid Fermentation_ is a bacillus 3 to 10µ in length, and about 1µ in breadth. It has power of movement, and when cultivated in gelatine, liquefies the gelatine, forming a scum on the surface. When the bacillus is sown into sterile milk, the following, according to Hueppe, are the changes: "If the milk thus infected is incubated, on the second day a clear, slightly yellow fluid is seen under the layer of cream; this fluid increases from day to day, so that gradually a column of fluid is formed which is quite clear above, but below is turbid; the casein, at first thrown down in a firm coagulum, in the course of eight days begins to be attacked, and by the end of two or three weeks most of it is dissolved. The filtered fluid gives the biuret reaction; it contains leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to some extent as a digestive of albumen. In advanced butyric acid fermentation, the fluid is most offensive, and may have an alkaline reaction." Lactic acid was first isolated by Scheele in 1780 from soured milk, but its exact constitution was not determined until later by Liebig, Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in nature, occurring in the sap of the vine and in most fermented liquids, especially in soured milk; it is not, however, present in fresh milk."[15] In all the Eastern preparations referred to, the lactic fermentation is produced, followed by alcoholic fermentation, which is due to the slow decomposition of the milk sugar, the vinous fermentation being most readily set up in milks which contain a larger relative proportion of milk sugar and water, such as the milk derived from the mare, the sheep, and the camel. As these fermented milks have different characteristics, it is necessary to the thorough understanding of the process of manufacture at the present day, to examine them in some detail.