No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 405 



Ehrlich-Biondi stain. The vacuoles are filled with a structure- 

 less fluid, which stains but lightly. But in four nuclei, the 

 sections of which were stained in aqueous solution of methylen 

 blue followed by brasilin, a differential stain of the ground sub- 

 stance was acquired : that pole of the nucleolus which con- 

 tained vacuoles was stained a bluish green (methylen blue), the 

 opposite pole, where no vacuoles could be seen, being of a light 

 pinkish color (brasilin), the vacuoles themselves appearing as 

 clear unstained spaces (Figs. 17-19). In one nucleus, in which 

 two minute nucleoli were present, the one without, the other 

 with, a single small vacuole, both nucleoli stained a bluish 

 green throughout (Fig. 18). Further, in an unstained nucleus 

 fixed with Flemming's fluid a somewhat similar differentiation 

 was visible in the two larger nucleoli (neither of which con- 

 tained vacuoles), the pole of each nucleolus nearest the nuclear 

 membrane being of a deeper color than the opposite pole (Fig. 

 1 1). This differentiation produced by staining would show that 

 the ground substance of the smallest nucleoli is homogeneous, 

 but that in the larger ones a chemical change takes place in it, 

 whereby that portion of the substance opposite the pole where 

 the vacuoles first appear differentiates itself chemically from 

 that portion of the ground substance lying at the latter pole. 

 Unfortunately I had too little material to carry further the 

 study of this differentiation. 



In the nucleus is a faintly staining nuclear sap, in which 

 irregular granules of various size are massed together espe- 

 cially near the center of the nucleus ; they do not come into 

 contact with the nucleoli, usually leaving a clear space around 

 each of the nucleoli (Figs. 7, 8, 11, 14, 17-19). These do not 

 stain with haematoxylin or with methylen green, but stain 

 red with eosin and brownish red with the Ehrlich-Biondi mix- 

 ture, in their staining differing little from the substance of the 

 nucleoli. With the methylen-blue-brasilin stain mentioned 

 above they stain pink, a little more deeply than does the inner 

 pole of each of the larger nucleoli (Figs. 17-19). Whether they 

 represent physiologically chromatin, or whether they are 

 masses of (perhaps nutritive) substance taken into the nucleus 

 from the cytoplasm, which might be chemically and genetically 



