6-5 THE YEAST CELL 



the fixed cells. It seems probable, therefore, that Kater ob- 

 served mitochondria in the living cell and destroyed them by fixa- 

 tion; he subsequently stained the chromosomes in the killed mat- 

 erial and identified the visible chromosomes in these preparations 

 with the mitochondria which he had seen in living preparations. If 

 he had employed the Feulgen stain, he would have avoided this error, 

 for it reveals the chromatinic threads as Feulgen-positive struc- 

 tures. 



Lindegren described the "chromatinic threads" which Wager 

 and Peniston observed in the nuclear vacuole as chromosomes be- 

 cause of their characteristic pairing and their characteristic chrom- 

 osomal morphology. Rafalko subsequently devised a modified Feul- 

 gen stain with which he stained chromosomes in Protozoa that had 

 previously been refractory to the Feulgen technique. He revealed 

 that both the "chromatinic threads," which Wager and Peniston had 

 demonstrated in the nuclear vacuole, and the centrosome were Feul- 

 gen-positive. Previous to his work, only the centrosome had taken 

 the stain and earlier workers had insisted that this, therefore, was 

 the true nucleus. Since his announcement, the new stain has become 

 widely used, and several unpublished reports of its superiority in 

 other material than yeast have reached us. Mirsky, Preer, and 

 others, in personal communications, have indicated their success 

 in staining Feulgen-positive structures with Rafalko' s more sen- 

 sitive Feulgen method. 



Previous workers have generally disagreed as to which struc- 

 tures in the yeast cell are chromosomes, centrosomes, or nucleoli; 

 the eccentric structure attached to the nuclear vacuole has been 

 called the "nucleus" by Guilliermond, the "nucleolus" by Wager and 

 Peniston, and the "centrosome" by Lindegren. The structure which 

 we consider the true nucleolus has only recently been demonstrated 

 by Rafalko to resemble a protozoan endosome for it is found within 

 the nuclear vacuole, is Feulgen negative, may contain plastin bodies 

 and is surrounded by a clear area which often has chromosomes 

 attached to it. We have concluded that the yeast cell contains a nuc- 

 leus composed of a hemispherical centrosome and nuclear vacuole; 

 the former contains the centroplasm, the heterochromatin, and a 

 central clear area; the latter the chromosomes and the nucleolus; 

 the cytoplasm contains the mitochondria. 



THE DIVISION OF THE CENTROSOME 



Badian (1937) (fig. 6-2), foimd that the centrosome (which he 

 called the "nucleus") contains two structures which take the Feulgen 

 stain. Badian developed an effective stain; he killed the cells with 

 osmic vapors, stained with methylene blue and destained with eosin. 

 He followed the centrosome in mitosis and meiosis in S. cerevisiae 



