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 Ambly- 
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, 82 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 w T as surprised to find that 
those fixed in the chromo-acetic-formalin mixture and 
stained in toto in Czoker’s alum cochineal show r ed Earyo- 
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 Ambly stoma tigrinum near the 
end of gastrulation were used. At this stage the egg 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-J per cent increase; in Kleinenberg’s 
fluid, 5 per cent decrease; in picric acid alcohol (0.2 per 
cent in 50 per cent alcohol) 8^ per cent decrease; in forma- 
lin-alcohol (commercial formalin 2 per cent 4 parts, 95 per 
cent alcohol 6 parts) 8^ per cent increase; in 4 per cent 
