146 



ANATOMY OF THE YEAST CELL. 



case of a Torula. An instructive example of this shedding the 

 membrane is afforded by Fig. 149. The separation (a, b) may 

 either begin at one spot and then gradually extend to a pro- 

 gressively increased peeling of the outer layer (up to 0.5 /x thick), 

 and the exposure of the inner and more delicate stratum of the 

 membrane ; or it may go on simultaneously all over the surface, 

 so that the cell remains enclosed in the unbroken outer layer 

 as in a bag {c), through which any daughter-cell that may be 

 produced has to make its way. Apart from such cases the 

 membrane of yeast cells is invariably closed on all sides. It is 

 neces.sary to emphasise this in view of Bizzozeko's (I.) impro- 



FlG. 149.— Permanent Cells of Bottom-fermentation Beer Yeast. 



a. The outer layer of the membrane beginning to peel off. Cell contents rich in 

 drops of oil. From a culture in beer wort. 



b The cell has perished from some unknown cause, before the bud in course of 

 formation had fully developed and separated therefrom. The dead plasma has collected 

 in lumps. The outer layer of the niemlirane has almost completely loosened, and en- 

 closes the cell like the caly.x does a flower. 



c A budding cell from which the exterior layer of membrane has become detached 

 on all sides. In this bag, wherein two daughter-cells are just commencing to separate, 

 rests the parent-cell, which is beginning to put forth a third new daughter-cell 

 through a crack in the outer membrane, b and e were taken from the yeast ring of an 

 old culture in peptone-dextrin-nutrient-salt solution. Magn. 2000. {After Will.) 



bable report that the membrane of a budding fungus found by 

 him in human epidermis — and of still indefinite position in the 

 botanical system — was full of pores. 



More or less perfect fragments of such discarded layers of 

 cell membrane are found in almost every liquid yeast culture of 

 a certain age. There is no danger of their being mistaken, 

 even by a beginner, for the albuminous flakes so common in 

 beer wort cultures, if microchemical reactions be called in aid, 

 since these will quickly show that we have here to do with a 

 substance differing both from albumin and from cellulose. 



With regard to the chemical composition of the materials 

 constituting the membrane of the yeast cell, there is not tuuch 

 reliable information to offer at present. Leaving out of con- 

 sideration what, in the present state of our knowledge, must be 

 regarded as an erroneous counter - opinion expressed by J. 

 ScHLOSSBERGER (I.), the absence of true cellulose therein was 



