156 



BACTERIA IN RELATION TO PLANT DISEASES. 



This fluid is transparent and slightly acid in reaction. 



To learn the microscopic structure he took single fresh lumps out of milk, washed them carefully 

 in water, then teased out portions with a needle and examined under a microscope fresh in water. 

 He also used various stains, such as carmine, picrocarmine, hematoxylin, eosin, purpurin, fuchsin, 

 aniline blue. Of these strains he found eosin best for the yeast-cells and fuchsin for the bacteria. 

 For more exact study of single forms he made use of cultures in hanging drops in Famintzin's moist 

 chamber. 



Kern states that the yeasts occur as single cells, pairs, and rows of cells, and are extremely 

 variable in form and size. He found them for the most part elliptical or spherical, but in nutrient 

 fluids he also often observed cylindrical cells or polygonal cells. 



The larger diameter of the elliptical cells varied between 3.2 and g.6M, the smaller between 3.2 

 and 6.4M. The spherical cells were 3.2 to 6.4^ in diameter, each cell had a plainly double contour 

 membrane. The protoplasm enclosed a vacuole. On the poles of the vacuole small dots of fat were 

 often to be seen. The well-nourished, normal cells reproduce by budding. Although he cultivated 

 his yeast-cells for weeks on potato and carrot, and pieces of black bread, he could never find any 

 outgrowth of the same into threads. He, therefore, concluded that he had to do with a genuine 

 yeast and not with any form of Mucor. He was not able to induce this yeast to produce spores, 



Fig. 38.* 



although he carefully followed the directions of Dr. Max Rees and Emil Schumacher. His cultures 

 remained in statu quo for weeks and then finally perished without formation of spores. He attributed 

 his failure to obtain spores to the fact that he had to do with the common cultivated beer yeast, 

 Saccharomyces cerevisiae. He states that in fermented milk the kefir grains sink to the bottom. On 

 the contrary in fresh milk they rise immediately to the top and remain there during the whole time 

 of the fermentation. [Buoyed up undoubtedly by the liberated gas.] 



Concerning the bacteria necessary to the ferment of the kefir grains Kern makes among others 

 the following observations. The vegetative bacteria have the form of short cylindric rods 3.2 to SM 

 long by O.SM broad. The inner structure of the cells appeared to be uniform, no inclusions having 

 been observed. The rods also may be separate or remain attached for a long time, in which case 

 they may form long threads. In the clumps of kefir one has unquestionably to do with bacteria in 

 the state of zoogloeae. Chloriodide of zinc does not react on the slime. In addition to the resting 

 zoogloeas stage, there is also a stage of motile cells, which cannot be distinguished from the other 

 stage in form or size. These latter are provided with one polar flagellum. The flagella were demon- 

 strated by Koch's early method, viz., by staining them for some time in extract of campeachy wood. 

 Exposed to the action of alcohol, Muller's fluid, various acids, or to drying, high temperature and 

 lack of food, the vegetative bacterial cells of the clumps are said to grow out into long Leptothrix 



*FiG. 38. (i) Kefir grains; (2) margin of a grain magnified to show relation of bacteria to yeasts. After Kern. 



