STATE GEOLOGIST. 179 



Up to the present time almost the only reagent which could be 

 employed for the instantaneous killing of Entomostraca with the 

 body in its natural position and the preservation of the same was 

 osmic acid, which partly on account of its expense, perhaps, seems 

 rarely to find its way into our laboratories. And even this is but 

 partially successful or causes such a dark color as to obscure what 

 one most desires to see. The desideratum seems to have been sup- 

 plied by the discovery of Prof. Hermann Fol that ferric perchioride 

 produces not only an instantaneous death but a fixation of all the 

 parts with very little coloration or shrinkage. The alcoholic solu- 

 tion is diluted to about 2 per cent, and applied to a small quantity 

 of water in which the animal is swimming, or a more concentrate 

 solution is added at once to the water of a vessel containing numer- 

 ous Entomostraca. The water is poured off and the animals washed 

 with alcohol of 70 per cent., to which a few drops of nitric acid 

 may be added to remove the ferric salts. According to Fol, in 

 transparent animals the appearance is very little changed by this 

 process. Specimens thus prepared may be preserved in alcohol 

 and afford preparations for making thin sections. They do not 

 take color well, but may be stained with gallic acid without diffi- 

 culty. 



As a preservative, glycerine does admirably for Copepoda, but no 

 known fluid works satisfactorily for the Cladocera unless after such 

 treatment as above indicated. Sections may be made by imbedding 

 in soap, but the tissues of the Cladocera are so delicate that the 

 writer never succeeded in making permanent preparations of such 

 sections. Either the alcohol or the balsam as it flows in almost in- 

 evitably disturbs the natural position. 50 grammes of soap are dis- 

 solved in 200 cu. cent, heated alcohol of 96 per cent. The soap 

 should be shaved very thin. A shallow paper trough is prepared 

 and filled with the still warm mixture, and the animal, which lies 

 in concentrated alcohol, is transferred into the solution and agitated 

 till its tissues are permeated with the soap. When cold, the bit of 

 soap is cut into the required form and is ready to be placed in the 

 microtome. 



As a preservative medium for Copepoda. Carpenters' gelatine an- 

 swers well. It consists of clarified gelatine, one ounce to six fluid 

 dramchs of pure glycerine. The preparations mounted in this re- 

 quire no cement, as the gelatine is quite firm when cold. 



