314 THE AMERICAN MONTHLY [Oct. 



of the leaf, are charged with a red cell sap of the nature of 

 glucosides. The cultivation of Hydrocharis morsusranoe, 

 of Utricularia, and many other land plants, in a weak solu- 

 tion of glucose, confirmed his deductions. In each case the 

 leaves assumed a rich reddish-brown tint. 



Chromic Acid. — For general botanical work the most 

 useful killing- and fixing- ag-ents are solutions containing 

 chromic acid. Prof. C. J. Chamberlain, g-ives some valu- 

 oble notes on the strengths of the solutions used. For 

 spirog-yra, fern prothallia, and similar objects, he sug-g-ests 

 a solution made up of chromic acid, two grammes ; acetic 

 acid, one cubic centimetre ; and water, ninety-seven cubic 

 centimetres. If plasmolysis takes place, weaken the chro- 

 mic, or strengthen the acetic, since the chromic has a ten- 

 dency to produce contraction, and the acetic to cause swell- 

 ing. Too large a proportion of acetic acid, however, may 

 cause distortion, and hence it would be better to weaken 

 the chromic acid. 



Fixing Tissues. — Referring to the time that should be al- 

 lowed for the fixing of tissues in chromic solutions, Prof. 

 Chamberlain has found that twenty-four hours should be 

 the minimum even for the most delicate objects. It is now 

 well-known that zoologists allow fixing agents like Muller's 

 fluid and Erlicke's fluid to act for weeks before the ma- 

 terial is passed on to the next stage, and it is therefore 

 questionable whether the time which is usually allowed by 

 microscopistswhenusingchromicacidsolutionsisnot much 

 too short. Sixteen to twenty-four hours is the time usually 

 allowed ; but Prof. Chamberlain's experiments show that 

 the material is better able to withstand subsequent proces- 

 ses if it has been kept in the fixing solutions for two or 

 three days. More rapid penetration, and consequently 

 more immediate killing, can be secured if the reagent is 

 kept at a temperature of from thirty degrees to forty 

 degrees Centigrade. 



Wickersheim's Preserving Fluid. — This is not com- 

 monly used owing to the poor preparations that have been 

 put on the market. Animal and vegetable bodies impreg- 



