130 The Microscope. 



acetic acid to ninety-nine or ninety-eight parts of distilled 

 water. For nuclear study, the cell or tissue may be fixed in 

 the above fluid and then placed in dilute glycerine in a watch 

 crystal so covered as to exclude dust but admit air. Here the 

 specimen should remain until the water has nearly evaporated, 

 at which time the preparation should be mounted in pure gly- 

 cerine (Dr. E. L. Mark). The evaporation of the water may 

 be accelerated by placing under the cover, calcium chloride, 

 caustic potash, or sulphuric acid which absorbs the water and 

 keeps the air dry. 



MIXTURES OF VARIOUS ACIDS. 



Osmic— Acetic Acid. — This most excellent medium is pre- 

 pared as follows : 



Osruic Acid, 1 % aqueous, 10 volumes. 

 Acetic " 2 " " 50 



Water 40 



As the action of this mixture depends on the nature of the 

 tissue, and the size and thickness of the piece treated, the 

 amount of osmic acid may be varied. If the preparation is too 

 dark and fine details too indistinct, the amount is lessened, if 

 too clear and evidently unaffected, more is added. For blasto- 

 derms and nuclear phenomena an immarsion of fifteen to 

 thirty minutes is sufficient. The tissue may then be washed in 

 a saline solution and mounted in glycerine, or hardened in 

 alcohol and teased out, or sectioned and mounted in balsam. 



Chromic — Acetic Acid. — This is of the highest value in the 

 study of cell life. 



Chromic Acid 1 %, 25 volumes. 



Acetic " 2 " 50 



Water 25 " 



This has been employed by Braun for embryos, by O. Hert- 

 ing for amphibian eggs and by Flemming for the asters in cell 

 division. When it becomes better known, this fluid will prob- 

 ably be of general value for vertebrate tissues. 



Chromo — Osmic — Acetic — Acid. — This is the most elegant 

 reagent which modern histological study has given us. For 

 cell study, Flemming recommends the following mixture : 



Osmic Acid 1 % , 10 volumes. 



Chromic " 1 " 25 " 



Acetic " 2 " 5 



Water 60 " 



