106 PROCEEDINGS OF THE AMERICAN ACADEMY 



I experimented with the Ontario material so far as to make sure that, 

 like the New Jersey form, it caused a fermentation of saccharose ; but 

 in studying the fermentation of other sugars I used only the New 

 Jersey form. 



When soaked for a time in water, the grains become whitish, very 

 firm and compact, and quite elastic. Examination under the micro- 

 scope shows them to consist of two elements, a small proportion of 

 yeast cells embedded in zoJgloea masses of rod-shaped Bacteria. 



Although in the dried specimens the ytast cells seem entirely dead, 

 yet when placed in a nutrient solution they begin to grow vigorously. 

 They vary in size and shape, from elliptical to spheiical, the aver- 

 age diameter of tlie latter being 4.2 fx, and the former varying from 

 10.5 ft to 6.0 /A by 6 /x to 4 /i,. On careful examination, each yeast cell 

 is found to have a plainly marked double contour, within which is an 

 almost homogeneous protoplasm containing a small vacuole. Culti- 

 vation of tlie yeast cells in water increases the size of the vacuoles, 

 and causes the formation of small fat globules at the poles ; and culti- 

 vation in strong solutions of saccharose produces two or even three 

 vacuoles in each cell, together with numerous fat globules. When 

 such cells are mounted in a mixture of acetic acid and glycerine, the 

 vacuoles disappear, and the protoplasm becomes finely granular. 



The yeast cells increase by budding, growing best in solutions of 

 dextrose and in milk, both of which they ferment ; and it is in these 

 substances that the best colonies are to be found. In pure water, the 

 yeast cells for a short time increase slowly in numbers by budding, 

 but no colonies are met with since the daughter cell separates from 

 the mother cell as soon as it is formed. In cane-sugar or saccharose 

 solutions, which the yeast is unable to ferment, the cells increase very 

 rapidly in numbers, but it is hard to find a colony of more than 

 three cells ; whereas in milk and in solution of dextrose, colonies num- 

 bering at least from ten to fifceen cells are very common. 



It was impo>sible to induce spore formation ; and indeed the very 

 fact that the yeast cells gave rise to new cells by the simple process of 

 budding after they had been dried for several months seems to war- 

 rant the conclusion that there is no spore formation. That they are 

 yeast cells, and not spores of Mucor racemosus or any otluT Mucor, is 

 shown by the fact that not a particle of mycelium was found during 

 the three months in which the yeast was under observation. 



Kern decided his yeast to be a form of Saccharonvjces cet-evisits, 

 Meyen. In the case of the North American kephir, the species evi- 

 dently is not S. cerevisicE, however much it resembles that species in 



