IOWA ACADEMY OF SCIENCES. 79 



subsequent staining, as witness most of the chromic acid 

 and osmic acid compounds. 



Some years ago I experimented on the eggs of Anihlij- 

 stoma with many of the fixing fluids commonly used by 

 cytologists. I used also a fluid recommended in the fourth 

 edition of Lee's Microtomist's Vade-Mecum, having the 



formula: 



Chromic Acid 2 per cent 64 parts. 

 Glacial Acetic Acid 4 parts. 

 Formalin, Commercial, 32 parts. 



At an early stage in the experimentation all fixing 

 fluids containing osmic acid and platinic chloride were dis- 

 carded, not only because of their imperfect penetration, 

 and on the part of osmic acid great blackening power, but 

 also because of their gelatinizing properties, causing the 

 embryos to adhere so firmly to the glass dishes containing 

 them that mutilation resulted on removing them. 



On sectioning the embryos I was surprised to find that 

 those fixed in the chromo-acetic-formalin mixture and 

 stained in toto in Czoker's alum cochineal show^ed Karyo- 

 kinetic figures in abundance and with great distinctness. 

 None of the other fluids used approached it in faithfulness 

 of preserving details. 



To determine the contracting or swelling effects of vari- 

 ous fixing fluids, eggs of Amhlijstoma tigrinum near the 

 end of gastrulation were used. At this stage the Qgg is a 

 nearly perfect sphere, containing a large cavity eccentric- 

 ally situated, so that one side of the egg is very thin- 

 walled. In this condition the embryo is very susceptible to 

 the shrinking or swelling effects of reagents. Eggs, all in 

 the same stage of development, were measured, and then 

 fixed and hardened for several hours, and finally measured 

 a second time. The following were the changes^in diame- 

 ter according to the fixing fluid used: 



In Perenyi's fluid, 7^ per cent increase; in Kleinenberg's 

 fluid, 5 percent decrease; in picric acid alcohol (0.2 per 

 cent in 50 per cent alcohol) 3| per cent decrease; in forma- 

 lin-alcohol (commercial formalin 2 per cent 4 parts, 95 per 

 cent alcohol 6 parts) Si per cent increase; in 4 percent 



