The Microscope. 249 



acid alcohol. 



Alcohol alone as a killing fluid is objectionable inasmuch 

 as it penetrates so slowty that the internal organs or portions 

 frequently undergo extensive alterations before they come fully 

 under the influence of the alcohol. When the stronger grades 

 are used the water is so quickly taken up by the alcohol on 

 account of the strong affinity of the two for each other, that 

 precipitates are produced which interfere seriously with subse- 

 quent manipulations and give many impressions. At the same 

 time the violent osmosis sometimes mechanically distends the 

 tissues, and the cells on account of the rapid and unequal actions 

 of this reagent, are almost always shrunken and the prepara- 

 tion valueless from a scientific point of view, for the true struc- 

 ture has been obliterated. 



These difficulties may be in a great measure obviated by 

 the use of the following mixture : 



Alcohol, 7 per cent 97 vols. 



Hydrochloric Acid 3 vols. 



The object should be placed in this until fully saturated, 

 and placed in pure 70 percent, alcohol until the acid is extracted 

 and stronger alcohol thus used to complete the hardening. Acid 

 alcohol should only be made as used, as in time ethers are 

 formed from the two separate reagents. This fluid may also be 

 used hot, it is then most efficient with insects, Crustacea, etc. 



GENERAL REMARKS ON KILLING FLUIDS. 



In preparing animal forms such as worms, leeches, embryos, 

 blastoderms, etc., for microscopical study, they should be 

 plunged alive into a large volume of the reagent selected, with 

 Crustacea and large forms generally, the body cavity should be 

 freely laid open so that the fluid may have immediate access to 

 every part ; or if certain organs only are wanted their cavity 

 may be flooded by means of a pipette. Or the fixative may be 

 injected through the blood vessels, or the alimentary canal 

 filled through a glass syringe. 



All organs (liver, kidney, spleen, stomach, etc.) of the 

 higher forms should be removed from the living or just killed 

 animal and subjected to immediate treatment. Any structure 

 of considerable size should be divided into small pieces so that 



