490 CHARLES H. SWIFT 



method, but the obscuring of the nucleus and cytoplasm by the 

 large, blackened yolk spheres is avoided. 



An ideal fixing fluid should not only be an excellent cytoplas- 

 mic preservative but should also have the ability to penetrate 

 rapidly. Unfortunately osmic acid and potassium bichromate 

 are lacking in this last quality. Acetic acid is frequently com- 

 bined with them because of its penetrating powers. However, 

 too much acetic acid is worse than none at all, since cytoplasm 

 and its contained organs, like mitochondria, are very sensitive 

 to this agent. For this reason Zenker's fluid is of no value in the 

 preservation of mitochondria. The acetic-osmic-bichromate mix- 

 ture of Benslej^ contains these fixing agents in about the proper 

 proportions, and yet even this leaves something to be desired. 

 It is of value as a fixative only when small pieces are used. It 

 really preserves, as in the natural state, only the outer surface of 

 a piece of tissue. In the center of a block of any size the mito- 

 chondria are found to be globular, instead of rod-like, or even 

 to have disappeared altogether. The value of the acetic-osmic- 

 bichromate mixture depends upon all the elements in it. They 

 do not all penetrate with equal speed; the acetic acid is much 

 the more rapid in this regard. Near the periphery of a piece of 

 tissue they act in unison, as is intended, but the acetic acid soon 

 forges ahead and acts in an injurious manner upon the cyto- 

 plasm and especially upon the mitochondria. 



The following staining methods were employed. Following the 

 Benda fixaton the Benda staining method was used. This pro- 

 cedure is the one commonly employed for demonstrating mito- 

 chondria. It was first published by Benda in 1901. 



Following Bensley's acetic-osmic-bichromate mixture two gen- 

 eral staining methods were used, namely, the anilin acid fuchsin- 

 methjd green method and Bensley's copper-chrome-hematoxylin 

 technique. There were, however, several modifications of the 

 first. In place of methyl green as a counterstain, toluidin blue 

 or Wright's blood stain may be substituted. Bensley ('11) de- 

 scribed these methods in detail, so there is no need to recapitulate 

 here. 



