The Microscope. 131 



For general histological use, killing all tissues preparatory 

 to further hardening, the following is perhaps a better one : 

 Osmic Acid 1 fi>, 2 volumes. 

 Chromic " 1 " 25 •« 

 Acetic " 2 " 5 " 

 Water 68 " 



The following mixture has been successfully used in study- 

 ing the ovary, and for the karyokinetic figures : 



Picric Acid, saturated aqueous solution, 10 volumes. 

 Chromic Acid, 1 % , 25 



Water, 65 " 



This is made more energetic by the addition of one volume 

 of a one per cent, solution of osmic acid. This reagent does not 

 interfere with the staining, but as it has small penetrating- 

 power, the pieces used should be quite small. 

 Chromic — Nitric Acid. — (Perengis Fluid). 

 Nitric Acid, 10 % , 4 volumes. 

 Alcohol, 3 



Chromic Acid, 5 %, 3 volumes. 

 This is of great value for embryological purposes, especially 

 for killing and hardening fish and amphibian eggs. These are 

 allowed to remain in the fluid 4 to 5 hours and then transferred to 

 alcohol until wanted. 

 MerheVs Fluid. 



Chromic Acid, 1:400. 

 Platinic Chloride, 1:400. 

 A mixture of equal parts of these fluids has been used for 

 hardening the retina, three to four days being allowed for the 

 action of the fluid. It is also a fluid which will find general 

 use as it becomes better known. 



This is a summary of the more valuable fluids which are 

 used for killing, some of them also suffice for hardening, but it 

 is better to employ other means to fit the object for section cut- 

 ting. In the next article the various methods of hardening and 

 embedding will be considered. 



KESOLUTION OF AMPHIPLEURA. 



ON a slide prepared by H. H. Chase, M. D., of Geneva, N.Y., 

 with a refractive index of 2.42, 1 have succeeded in clearly 

 resolving A. pellucida with a dry 1-5 in. of 135° air angle. This 



