The matrix is composed entirely of long thin bacilli (_Bacillus caucasicus_), while the peripheral portions, which are more deeply stained, consist to a large extent of dense masses of yeast cells with occasional streptococci. In a normal grain the latter organisms are present on the surface or in the cavities and grooves of the grain, and only to a less extent in the matrix. Nikolaiewa[57] claimed to have isolated a hitherto unknown bacillus capable of coagulating milk by acid production, _Bacterium caucasicum_, not identical with, but related to Freudenreich's _Bacillus caucasicus_, and also a torula. Although no experiments were carried out, Nikolaiewa asserts that this organism forms the matrix of the grains. He was able to produce a beverage resembling keffir, just as Freudenreich and Essaulow did with entirely different organisms, but his product would appear to have been slightly too acid and to have lacked the characteristic aroma of the normal product. In the course of an extensive series of experiments Kuntze[58] found the following organisms: (_a_) True lactic acid forming bacteria, _Streptococcus acidi lactici_ (Grotenfeldt). (_b_) Bacteria of the group _Bacterium acidi lactici_ (Hueppe) and _Bacterium lactis aërogenes_. (_c_) Various torula and yeast species. (_d_) Two species of butyric acid bacteria, _Bacillus esterificans_ and _Bacillus keffir_ (Kuntze). His conclusions are: 1. In any case the presence of a yeast capable of directly fermenting milk sugar is not essential. 2. The significance of the presence of yeast lies in the fact that stimulation of the lactic bacteria occurs; further, the yeast exerts a regulating influence upon the rapidity of the fermentation proper. The variety is of minor importance, provided always that the yeast does not produce an unpleasant flavour. By the use of mixed cultures of _Bacillus esterificans_, _Bacillus keffir_, and _Streptococcus acidi lactici_, and a keffir yeast, Kuntze obtained a product that possessed to the fullest degree all the characteristic properties of a normal keffir. In such cultures he was successful in obtaining the formation of keffir-like grains. Keffir fermentation is, according to Kuntze, the result of the action of various organisms. During the initial stage butyric acid fermentation takes place, but is prevented from becoming predominant by the action of the keffir yeast. Simultaneously a true lactic acid fermentation proceeds and eventually gives place to a subsequent secondary production of butyric acid. Finally, then, we have a certain amount of unison in the results obtained by Freudenreich, Essaulow, Nikolaiewa, and Kuntze. These show that, for the production of a characteristic keffir, specific organisms are not essential, provided always that those used possess, either individually or collectively, the essential capacity of acidifying, coagulating, and fermenting the milk. For the growth of normal grains the presence of a matrix-forming