212 CORA J. BECKWITH 



apparently differential stain may be obtained on coagulated 

 egg-albumen which may depend on purely physical differences or 

 differences in density. Experiments were also made to test Hei- 

 denhain's contention that selective staining is most successful 

 when the stains are applied simultaneously and progressively. 

 Since different results are obtained when stains are used succes- 

 sively, sumultaneously, progressively, or regressively, a true 

 selective value can hardly be maintained. The evidence from 

 all sides indicates that staining reactions are unreliable as chemi- 

 cal tests. 



6. Artificial peptic digestion tests were tried to determine if 

 possible, whether the granules are chromatin (table 2). If one 

 accept the non-digestion of any material in the cell as proof of its 

 chromatic character, then thife test supports the nuclear origin 

 of the granules. Material killed in alcohol and in boiling water 

 as well as fresh material, was used in these tests. The fixed 

 material was sectioned and digested on the slide in a 1 per cent 

 solution of pepsin in a i per cent solution of hydrochloric acid. 

 Such digested sections together with an undigested control were 

 stained with iron-hematoxylin and light green or with Auerbach's 

 fluid. The fresh material was stained both before and after 

 digestion with acidulated methyl-green, Auerbach's fluid, new 

 methylene-blue G.G., new methylene-blue R., and diamond 

 fuchsin, and mounted in glycerine. In all cases, after two to 

 three hours of digestion at body temperature, the yolk, mitochon- 

 dria and the bulk of the protoplasm were digested in the adult 

 egg, leaving a slight framework or net which stained only with 

 plasma stains. In the young eggs the protoplasmic granules re- 

 main undigested and. take the basic stains, while the nucleus is 

 non-staining. This reversal in staining of digested material as 

 compared with fresh material when stained with the same neutral 

 vital stains may well be due to the acid in the digestive medium, 

 a point which supports the view that staining depends on previous 

 treatment. 



Even though the granules in fixed material, whether digested or 

 undigested, stain with basic dyes, a slight difference between the 

 two occurs. If two slides, one containing digested, the other undi- 



