nORMANCy 8 -4 



cent of the cells from the Warburg vessel showed little or no 

 change. 



Cells of a standard baking yeast, strain A, which had been grown 

 on pre-sporulation agar, were collected from the agar surface and 

 washed with M/15 KH2PO4. Three Warburg vessels were inoculated 

 with equal amounts of dormant cells. Each vessel contained 4 per 

 cent of glucose in solution. The first received phosphate buffer, the 

 second received 1 per cent of corn-steep-water solids, and the third 

 received 0.3 per cent ammonium sulfate, biotin (2 y per liter) and 

 pantothenic acid (200 y per liter) (fig. 8-2). 



Since our culture of S. cerevisiae is a "non- synthesizer" of bio- 

 tin and pantothenic acid, these substances were added, together with 

 ammonia, to see if they would break the dormancy of the fat-filled 

 yeast cells. The cells suspended in buffer were dormant and gave 

 off no CO 2 after over five hours in the Warburg apparatus; but the 

 cultures in the other vessels fermented the sugar, the action being 

 much more rapid in the richer nutrients. This experiment cannot 

 always be duplicated because cells from the pre-sporulation agar 

 slants are not always in precisely the same condition for some cul- 

 tures sporulate directly on the slant and in some cultures all the 

 cells do not fill uniformly with reserves. 



FORMATION OF FAT AND MITOCHONDRIA 



Formation of fat and mitochondria occurs most rapidly in a 

 medium in which fermentation and growth have nearly ceased. A 

 1 per cent glucose broth was prepared with half the standard 

 amount of nutrient broth to insure the early cessation of growth. 

 Fifty ml. of broth in 500 ml. Erlenmeyer flasks were inoculated 



Fig. 8-1 1. Budding vegetative yeast cells at the loga- 

 rithmic stage oi growth showing a single vacuole cliarac ter is t ic 

 of this condition. 



2. Budding yeast cell m the lag pliase showing 

 the apparently multiple vacuole resulting from deformations of 

 the single vacuole by interference of reserve material. 



3. Dormant vegetative yeast cells loaded with 

 mitochondria and glycogen, grown on presporulat ion agar; the 

 dark color is glycogen stained with iodine. 



4. Germinating dormant cells from [iresporula— 

 tion agar, showing the vacuole spreading through tlie enclosing 

 net— work of mitochondria and glycogen. 



5. Cells loaded with mitochondria by growth in 

 aerated gugar solution. 



6. Cell of the type shown in 5 germinating. 



7. Cell grown in sugar under conditions of re- 

 duced oxygen tension loaded with glycogen, a few mitochondria 

 surrounding vacuole. 



R. Cell of the type sliown in 7 stained with 

 iodine, revealing the deformation of the vacuole by the reserve 

 materials . 



