cyroLOGY 6-28 



visible simultaneously. The cytoplasm Is pink, Indicating the pre- 

 sence of ribosenucleoproteln In the cytoplasm. The green colora- 

 tion of the centrosome and chromosomes Is consistent with the view 

 that both contain chromatin. The green color of the nucleolus sug- 

 gests that It may also contain chromatin on occasion. This view 

 has been supported by the Feulgen stain which has on rare occa- 

 sions seemed to reveal pink colored nucleoli. 



The Feulgen method often stains the centrosome without stain- 

 ing the chromosomes; or the chromosomes may be stained while 

 there is little or no stain in the centrosomes. We have rarely ob- 

 served a pink coloration with Feulgen in the nucleolus, but have 

 never foimd all three structures Feulgen -positive simultaneously. 

 Chrome -acetic -formaldehyde followed by Feulgen and fast green 

 reveal a typical Feulgen purple-red in the centrosome. The chro- 

 mosomes were somewhat refractile and red-red, rather than the 

 characteristic purple-red. The chromosomes were also a much 

 fainter color than the purplish Feulgen-posltlve structures in the 

 centrosome. Carnoy material stained with Feulgen shows the cen- 

 trosome with excellent detail and reveals the crescent-shaped bodies 

 so often described by earlier workers in the centrosome. Carnoy, 

 however, is a poor fixative for vacuole and chromosomes; in fact, 

 they are rarely visible after Carnoy. Chrome-acetic -formalde- 

 hyde is an excellent fixative for chromosomes. When the Feulgen 

 stain was used on S. cerevisiae, Mrak 77 following mercuric chlo- 

 ride fixation, only the centrosome appears to take the Feulgen stain 

 (these stains were made after 1 to li hours). When, however, mer- 

 curic chloride and chromic acid are used in the killer, the centro- 

 some is visible, with chromosomes occasionally visible in the same 

 cells. Carnoy fixation followed by Feulgen and fast green has shown 

 the nucleolus occasionally to be refractile and faintly pink. The 

 following tabulation shows the results with different varieties of 

 yeasts. 



The demonstration of a structure in the nuclear vacuole iden- 

 tified as the nucleolus associated with Feulgen-posltlve threads 

 confirms the view that the Feulgen-positive threads are chromo- 

 somes and eliminates the possibility that the Feulgen-positive 

 structures in the centrosome are chromosomal. This suggests 

 that the centrosomal chromatin may be the equivalent of the het- 

 erochromatin in higher organisms. The apparent shifts of chro- 

 matin from chromosomes to centrosome andy/ce versa suggest 

 a cyclic relation between the chromosomal and the centrosomal 

 chromatin, and the fact that the nucleolus sometimes, though 

 rarely, contains chromatin suggests that it may be involved in 

 the cycle. 



