7-5 THE YEAST CELL 



integration or solution, with a decrease in the density of the glyco- 

 gen mass. Finally a single large diffuse granule is found in the 

 cell, and the vacuole regains its original size. Under favorable con- 

 ditions, involving low oxygen tension and continued addition of sugar, 

 all the cells may become filled with glycogen. 



Stainable glycogen does not accumulate in well -aerated yeast 

 cultures grown in 1 per cent glucose broth. The nuclear vacuole 

 attains its maximal size under these conditions. 



Some dead cells contain glycogen in their vacuoles. Most of 

 the dead cells remaining in a culture, which has grown until all the 

 glycogen has disappeared from the living cells, contain glycogen in 

 the cytoplasm. Either glycogen tends to deposit in dead cells or 

 dead cells are unable to metabolize their accumulations of glycogen. 



When a cell is fixed with formalin and stained with iodine the 

 chromosomes often turn dark brown suggesting that they may con- 

 tain carbohydrate on occasion. (See chapter 6.) 



MITOCHONDRIA 



The cytoplasm of the yeast cell contains many mitochondria if 

 the culture is well aerated and well supplied with phosphate and 

 sugar. The mitochondria contain fat and ribose nucleoprotein. When 

 the cell is fermenting rapidly mitochondria are not visible. Staining 

 with Nile -blue sulphate and osmic acid generally indicates that the 

 fat is also evenly distributed throughout the cytoplasm. The mito- 

 chondria are often deposited at either pole of the vacuole, or com- 

 prise a network of streptococcal like threads of granules which 

 sometimes branch and are closely appressed to the outer surface 

 of the vacuole. In most types of S. cerevlsiae the mitochondria tend 

 to increase in numbers and to enlarge individually as the culture be- 

 comes older and storage increases. The addition of alcohol or the 

 application of heat causes many of the globules to coalesce. Dead 

 cells usually contain coalesced globules, just as they often contain 

 glycogen. Mitochondria invariably accumulate in yeast cells grown 

 in shallow well-aerated Erlenmeyer flasks. Mitochondria appar- 

 ently contain fat together with ribose nucleoprotein and may pro- 

 vide a mechanism for storing the reserve ribose nucleoprotein so 

 that it is not in contact with the cytoplasm directly and therefore 

 inactive in metabolism. 



Wiame (1947) has defined the total basophily of a yeast suspen- 

 sion in terms of the total amoimt of toluidine blue taken up by a 

 given amount of cells from a standard concentration of the dye. He 

 dries a suspension containing a known number of cells on an etched 

 glass slide. Then he stains the dried smear with toluidine blue. 

 The suspension is next washed with normal hydrochloric acid and 

 becomes completely destained. The amount of dye taken up is col- 

 lected and measured arbitrarily in a photoelectric colorimeter. 



