SYMBIOSIS. 155 



BACTERIAL SYMBIOSIS IN CRYPTOGAMS. 



Bacteria with Yeasts. 



KEFIR. 



Kefir is a granular gelatinous substance, horny when dry, occurring naturally in 

 the Caucasus. It has been known for centuries and used extensively to make a fermented 

 drink from milk alcohol, carbon dioxide, and lactic acid being produced. The substance 

 is said to occur naturally on peculiar bushes just below the snow line in the mountains 

 (Mix) but this is probably folk-lore. Gradually a knowledge of the substance diffused 

 into Europe and it may now be had in many places. Beyerinck states that it is identical 

 with the ginger-beer plant of England, the kefir having been brought back from the Crimea 

 by the English soldiers. Beyerinck's figure of kefir differs so much, however, from the 

 figures and description of the ginger-beer plant published by H. Marshall Ward that they 

 would seem to be two different substances. Many papers have been published on kefir. 

 The chemistry of the action appears to be better known than the specific organisms which 

 enter into the composition of kefir. 



Kern was the first botanist who called general attention to the morphology of the 

 substance. He found it to be composed of yeast and bacteria in what he believed to be 

 a symbiotic relationship. He considered the yeast to be the common beer yeast, Saccharo- 

 myces cerevisiae. He described the Schizomycete as Dispora caucasica. This schizomycete, 

 he stated, commonly produces a spore in each end of the rod, the diameter of this spore 

 being not greater than the rod itself. 



The substance of Kern's paper is given in the following abstract : 



Kern observed kefir in the Caucasus in the summer of 1881. The mountain people make large 

 use of milk as food, but they do not use the milk to any great extent in a fresh condition, first fer- 

 menting it in leathern sacks by means of grains of the kefir. The kefir fermentation goes on more 

 rapidly if a large number of grains are put into the milk. Ordinarily the kefir is ready to use in a few 

 hours, the leather sack first being shaken thoroughly before it is poured out. After the kefir is poured 

 out of the sack the latter is filled with fresh milk. 



"When the kefir preparation has succeeded it is a thick fluid mass without any large coagulated 

 lumps, agreeably sourish in taste. By a longer fermentation it is converted into a mossy, foamy, 

 strongly acid drink, which is similar to the Kumys of the Steppe region. " 



The dwellers in the mountains use the kefir not only as food, but also as a medicine in various 

 diseases with results, believed to be superior to those obtained with Kumys. Kern states that he 

 was unable to find any scientific data on the subject. He states that the physiological and thera- 

 peutical action of the kefir is a thing to be studied by a physician. He devoted himself to an exam- 

 ination of the microscopic structure of the kefir grains and the morphological nature of the ferment. 



"The little clumps form white, compact, elastic masses, covered over with slime. They have a 

 spherical or elliptical form and a size of 1 mm. to 5 cm. Quite small lumps have a smooth, spherical 

 exterior, the larger on the contrary, are provided with various protuberances and furrows (fig. 38) 

 and in appearance are not unlike a cauliflower head. " 



In every such lump, no matter what its form or size, the microscope shows two different structures 

 that is, yeast-cells and bacteria. The yeast-cells are inclosed in groups here and there in the mass of 

 the bacteria. 



For his mass-cultures Kern used nutrient fluids, at first Pasteur's fluid, composed of 1,000 grams 

 of water, 100 grams of candy sugar, 1 gram right ammonium tartrate, and the ashes of 10 grams of 

 yeast. Subsequently he confined himself exclusively to Cohn's normal bacterial nutrient fluid 

 (Untersuchungen, Bd. I, Heft 2, p. 196), and like Eidam recommends substituting for the insoluble 

 tribasic phosphate of lime, equal quantities of calcium chloride. This fluid is only adapted to the 

 nourishment of the bacteria. For the needs of the yeast he added milk-sugar, in about the quantity 

 found in milk. The nutrient fluid which he used for the most of his cultures had, therefore, the 

 following composition : 



Distilled water 1000 



Milk-sugar 44 . 5 



Ammonium tartrate 9 



Calcium chloride 0.5 



Magnesium sulphate 5 



Phosphate of potash 5 



