480 GENETICS OF SOMATIC CELLS 



fact, our present data (unpublished) indicate that this is much too simple a hypothesis 

 for such a complex tissue." Could it be that the chromosome numbers of the bone- 

 marrow complex vary purposefully as a prelude to inaugurating the various and 

 complex processes of differentiation? Weicker and Terwey 1369 have reported an 

 extreme variability in the chromosomal number of bone-marrow cells of the Chinese 

 hamster. The slight aneuploidy observed in bone marrow of normal Chinese hamsters 

 by Tonomura and Yerganian 1324 probably are similar to human derivatives in this 

 respect. 



Stains.— The use of aceto-orcein or acetocarmine, with or without phase micro- 

 scopy, has eliminated the need to undertake the more time-consuming Feulgen staining 

 for routine investigation. Although orcein and carmine are more versatile, Lacmoid, 

 Dahlia Blue, Chlorazol Black E, and Sudan Black have been utilized occasionally. 

 The use of nondecolorized basic fuchsin for staining of murine pachytene chromosomes 

 has been found satisfactory by Slizinski 1217 and Jaffe. 660 A general reference recom- 

 mended for staining procedures is the compact and revised report by Darlington and 

 LaCour. 239 



The selection of a stain is regarded as a personal choice, rather than one of tried 

 experimental comparison. Acetocarmine and propionocarmine are considered by 

 the writer to be far more favorable for mammalian chromosomes than aceto-orcein, 

 customarily recommended for this type of work. When viewed with phase micro- 

 scopy, carmine is excellent. When employing procedures described below, carmine 

 rarely fills the matrical portion of the chromosomes when limited to 30 seconds of 

 staining, as contrasted to orcein which stains the chromatin as well as the pellicle or 

 matrix deeply. The carmine-stained chromatid appears minimal in diameter, as in 

 the case of Feulgen stain, when compared to that noted after orcein-stained trials. 

 The finer details of chromosomal structure, that is, heterochromatic versus euchromatic 

 areas, are readily visualized with light carmine stain. Excessive mordanting (see 

 below) and lengthy periods of staining generally lead to a masking of all important 

 structural entities. This may be illustrated by the fact that the distinct features of the 

 mitotic sex chromosomes were not recognized readily during the past decade, although 

 a myriad of rodent metaphases were viewed by well informed cytologists. A similar 

 trend is now occurring in the study of human mitotic chromosomes. The majority 

 of the cells were heavily stained with orcein and viewed either by bright-field or dark- 

 contrast, phase microscopy. The writer considers the use of light-carmine staining and 

 medium-to-light contrast, phase microscopy a great help in revealing heterochromatic 

 portions and sex elements of Chinese hamster and human derivatives (figures 63, 64, 

 and 65). 



R. Lang (personal communication) has experienced no precipitation of synthetic 

 aceto-orcein when using 85 per cent lactic and glacial acetic acids. Equal volumes of 

 the acid solutions are warmed almost to the boiling point in a water bath prior to 

 adding the appropriate amount of stain. The mixture is left to cool, then filtered and 

 stored. Following this type of preparation, orcein fails to precipitate and slides resist 



