388 Pierre A. Fish 



ural changes induced thereby, it is advisable to use not 

 higher than ninety per cent. The great and unequal attrac- 

 tive power of alcohol for water, renders it necessary to begin 

 with the lower grades. Otherwise the rapid withdrawal of 

 the water before the alcohol can replace it, will cause shrink- 

 age and the tearing or breaking down of the tissue. Immer- 

 sion of a large specimen in a limited quantity of strong al- 

 cohol is likely to induce a rapid hardening of the surface, 

 forming a crust through which the alcohol maj' cease to pene- 

 trate, causing a consequent maceration of the interior. 



For general utility, economy and certainty of result, no re- 

 agent excels potassium bichromate in its action on nervous 

 tissue. It is said that attention was called to this salt for 

 hardening purposes by a Mr. Savory, some thirty or more 

 years ago'". It is commonly used in a simple two or five per 

 cent, solution or in the form of " Miillers " or "Erlicki's" 

 liquids. The simple solution has of late come into greater 

 prominence. 



It is inexpensive ; it hardens slowl3^ but thorough!}-, with a 

 minimum of distortion and leaves the specimen in a state of 

 good consistency even if its action is prolonged. Its applica- 

 tion is general ; it preserves the contours of large and 

 irregular areas for the morphologist and maintains the proper 

 relations of the structural elements for the histologist. A 

 little chromic acid (one or two drops of a one per cent, 

 solution) added to each thirty cubic centimeters of the 

 bichromate will do no harm and will quicken the hardening. " 

 All chromic salts impart a disagreeable and abnormal color to 

 the specimens and for some purposes render them quite un- 

 desirable. 



This"" it is said may be obviated to some extent bj' harden- 

 ing the tissue in the following mixture : 



Potassium bichromate 6 grams 



Potassium nitrate 4 grams 



Water 180 c. c. 



After-treatment with absolute alcohol is recommended by W. 

 C. Krauss for decolorizatiou. Unna advises peroxide of 

 hydrogen. Lee mentions chloral hydrate in a one per cent. 



