452 GEORGE A. BAITSELL 



With regard to this combination, it may be well to say in the 

 first place that, of all the preserving fluids tried, Zenker with 

 acetic gave the best results. The only objection to this fluid 

 is that it has a tendenc}^ to harden the yolk material in the 

 embryos somewhat more than some of the other fluids and this 

 makes the sectioning of the earlier stages difficult. However, 

 the difference here is not great and the superior preservation in 

 the Zenker fluid warrants its use. 



As to the staining, it was found that the JNIallor}^ connective 

 tissue stain was superior to any of the other stains tried for the 

 work in hand. A comparative study was made of the reactions 

 of this stain as originalh" given and the same stain as modified 

 by Mall ('01-'02). The results obtained show very clearly that 

 the modified Mallory does not give such a clear differentiation 

 between cytoplasm and ground substance as does the original 

 Mallory stain. Mall says,^ "My best specimens were obtained 

 by staining the sections with ^Vlallory's connective tissue stain 

 which tinges the nuclei and surrounding endoplasm, if present, 

 slightly red and the exoplasm of the syncytium intensely blue. 

 We have modified this stain somewhat by omitting the water 

 and int nsifying the blue." 



The results of the comparative study have convinced me that 

 the intensification of the blue is a mistake in that thereby the 

 differentiation between the cell cytoplasm and the ground sub- 

 stance of the developing connective tissue is largel}^ lost. In 

 material preserved in Zenker and correctly stained with Mal- 

 lory's original stain there is a clear differentiation between the 

 cells, which are of varying shades of red, and the ground sub- 

 stance which is invariably blue. It is possible therefore in such 

 material to speak with certainty as to the limits of the cell 

 boundaries and the relations the cells bear to the common inter- 

 cellular ground substance. When the blue is intensified the 

 entire field takes this color and the differentiation becomes 

 obscured or even lost. 



5 Mall, 1902, p. 338. 



