MORPHOLOGY AND ANATOMY OF YEAST CELLS. 291 



budding fungi, one of which is represented by S. cerevisice /., 

 the second by the three Pastor 'ianus species, and the third 

 by both the ellipsoideus species. So much and no more 

 can be established by a purely microscopical observation, 

 and this only under the particular culture conditions described. 



The development of the yeast cell takes place through 

 budding, a slight swelling appearing in the mother cell, which 

 increases in size. According to Kny, budding follows with 

 equal rapidity both in light and darkness. As soon as the 

 new cell has attained a certain size it can form a new bud, 

 and this process of budding continues until a group of budding 

 cells is formed. The cells may break away from each other 

 at an earlier or later stage, so that the group may consist of 

 a varying number of individuals. The development of the 

 yeast cell was observed by Mitscherlich in 1843. The daughter 

 cell may assume a totally different form from the mother cell. 

 This may also take place in the industrial species, including 

 those which give fairly uniform oval cells in the large fermenting 

 vats. For example, ordinary brewery, low-fermentation yeast 

 may, for reasons unknown, produce cells with the appearance 

 of Pastorianus and ellipsoideus, so that it is impossible, under 

 the microscope, to distinguish whether such a culture yeast is 

 infected with a foreign yeast or not. 



As an example of the change of form brought about by an 

 unknown cause in the case of industrial yeast, it may be men- 

 tioned that, by excessive treatment with air, .the air-yeast 

 of the pressed-yeast factory alters from an oval or elliptical 

 to a much elongated Pastorianus shape. 



In general, it may be stated that low-fermentation yeasts 

 form groups containing fewer cells than is the case with top- 

 fermentation yeasts. There are, however, many exceptions 

 to this rule. It is impossible to indicate any universal type 

 of microscopical picture for the two groups of yeasts, and 

 the same holds good for the general picture of a single race of 

 culture yeast. It is only by exactly comparable growths 

 carried out in parallel experiments in the laboratory that it 

 is possible to establish differences between the general appear- 

 ance of the races. When applied in practice, so many different 

 factors come into play that the appearance of the growth may 



