1 62 BACTERIA IN RELATION TO PLANT DISEASES. 



and hence called "Millet of the Prophet;" (2) the grains were found very long ago in a bush 

 on the high mountains near the eternal snow ; (3) the first grains appeared in a dirty milk 

 receptacle (outre). "Cette derniere version populaire se rapproche beaucoup, a notre 

 avis, de la verite." 



According to Podwyssotsky, the kefir grain is composed of three organisms : The kefir bacterium 

 proper, the yeast, and a third schizomycete which produces the lactic acid. He states that Stanghe" 

 was the first to call attention to the presence of a third organism in kefir. The yeast cells are on the 

 outer face of the grains. The deeper layers consist of a fibrous stroma of bacteria. This author states 

 that healthy kefir grains never contain streptococi nor staphylococci. He is inclined to consider the 

 the kefir bacteria as related to Bacillus subtilis (descended from it). He states that the yeast re- 

 sembles Saccharomyces cerevisiae in its action. Moreover, if the alcoholic action of the kefir in milk 

 is not proceeding properly it may be hastened by the addition of ordinary beer yeast. Podwyssotsky 

 also refers to the fact that there appear to be two types of kefir grains ; a coarse large form which 

 comes to the top of the milk during fermentation, and a smaller grained form which lies at the 

 bottom. These have the same action on the milk. The grains which occur at the bottom of the 

 milk break apart more easily when pressed between the fingers and are not as elastic as those which 

 float. 



The kefir grains, especially as brought into the market dry, are often attacked by other organisms 

 e. g., Oidium lactis, Penicillium glaucum, coccus forms, and various rod-shaped bacteria. A cursory 

 inspection of these grains is often sufficient to show that they are diseased by these extraneous organ- 

 isms, the surface of the dry grains being covered with white spots. If the grains are dried slowly in 

 a moist and shady place, they often become very moldy and exhale a characteristic and very dis- 

 agreeable odor. 



He recognizes especially two diseases of the kefir fermentation : 



(1) Mucification of the grains due apparently to the multiplication of foreign bacteria, the yeast 

 cells being destroyed, and spherical and long filamentous bacteria becoming abundant. This is 

 believed to be a contagious disease since, if a single affected grain occurs in a mass of grains, there 

 will be many others after some days. 



(2) A butyric acid fermentation which may be readily detected by the peculiar penetrating 

 odor, resembling that of rancid butter. Moreover, microscopic examination of a drop of the fer- 

 mented milk shows the presence of a great number of bacteria with swollen ends while the yeast cells 

 have here also disappeared. 



On account of the prevalence of extraneous molds and bacteria, kefir grains designed for sale 

 dry should be washed thoroughly in several waters, i.e., until the water conies away clear, and then 

 dried rapidly in the sun on linen or filter paper. 



Podwyssotsky states that the kefir ferment may be obtained in various places in Europe in the 

 form of tablets and powders. These are not so efficient as the kefir grains, but by several transfers 

 through milk the kefir ferment may often be obtained from them in an active condition. The first 

 product is usually too acid and does not contain enough carbon dioxide and alcohol. Much of the 

 kefir on the markets in Russia is contaminated by butyric acid organisms and is of very inferior 

 quality. Many of the kefir grains offered for sale are also of this character. 



The best temperature to obtain a suitable kefir fermentation of milk is stated to be 15 to I7C. 

 At temperatures of 25 to 30 C. the lactic acid fermentation is too intense and only insignificant 

 quantities of alcohol and carbon dioxide are produced. Frequent agitation of the receptacle con- 

 taining the fermenting milk is considered to be very desirable ; more so, even, than in the case of 

 Kumys. The author states further that the inoculated milk should be left open to the oxygen of 

 the air for the first 6 to 8 hours, then closed tightly and the fermentation allowed to continue for i or 2 

 days. The finished kefir should contain about 0.7 to 0.9 per cent lactic acid, a small amount of pep- 

 tone, 1.5 per cent or less of alcohol and considerable quantities of carbon dioxide. Kefir more than 

 5 days old should never be consumed. A drop of good kefir 2 days old under the microscope should 

 contain some yeast cells, considerable numbers of kefir bacteria, numerous minute lactic acid 

 bacteria, a fine deposit of precipitated casein, and fat drops of various sizes. Kefir grains moistened 

 and rubbed upon a slide should show under the microscope yeast cells, large bacteria (the specific 

 kefir organism), and smaller lactic acid bacteria. In a drop of kefir 8 days old, the lactic acid bacteria 

 are very abundant and the yeast cells have entirely disappeared. 



THE GINGER-BEER PLANT. 



The following account of the ginger-beer plant, and the organisms composing it, is 

 condensed from H. Marshall Ward's long paper in the Transactions of the Royal Society 

 of London. 



