APPENDIX II 693 
It is used in 1 to 2 per cent. solutions and should be made up in 
distilled water. It fixes cytoplasm well but the nucleus not as 
good. Its disadvantage lies in its inability to penetrate rapidly. 
Chromic acid (CrOs) in 0.5 to 1 per cent. aqueous solution is 
very favorable for nuclear structure but like osmic acid penetrates 
rather slowly. | 
Picric acid CsH2(OH)(NOz)s; is one of the most penetrating 
fixing fluids but has very little hardening power. It is employed 
in saturated aqueous solution. 
Corrosive sublimate (HgClz) in 0.2 per cent. aqueous or alcoholic 
solution penetrates and hardens rapidly but does not give as sharp 
optical differentiation as the others considered. 
Absolute alcohol can be employed for very small objects that 
are dry. If the objects are moist, shrinkage will follow. 
Carnoy fluid, consisting of 6 parts absolute alcohol, 3 parts 
formaldehyde and 1 part of glacial acetic acid, can also be used 
for fixing small objects. It has the advantage of fixing these in 
about 10 minutes. Moreover, the objects can be carried directly 
to absolute alcohol, thence to hot melted paraffin and imbedded. 
Chrome-acetic-formalin fluid (Craf Fluid). This comparatively 
new fluid has been found to give very favorable results in fixing 
materials for chromosome studies. The chromosomes are better 
defined after staining with Heidenhain’s hematoxylin and give a 
good contrast with the cytoplasm. It is prepared by mixing 
equal volumes of the following solutions designated as Solution A 
and Solution B just before using. Solution A contains chromic 
acid, 1 Gm., glacial acetic acid, 7 cc. and distilled water 92 cc. 
Solution B contains neutral formalin (40 per cent. formaldehyde 
solution) 30 cc. and distilled water 70 cc. The material to be 
fixed should be placed in this fluid for from 12 to 24 hours after 
which it can be directly transferred to 75 per cent. ethyl alcohol, 
changing the solution every 15 mi. for 3 or 4 changes, thence to 
85 per cent. alcohol (1 hr.) to 65 cc. of 80 per cent. ethyl alcohol 
and 35 cc. n-butyl alcohol (1 hr.) to 45 cc. of 90 per cent. ethyl 
alcohol and 55 cc. of n-butyl alcohol (1 hr.) to 25 cc. absolute 
ethyl alcohol and 75 cc. n-butyl alcohol (1 hr.) to n-butyl alcohol 
for 2 or 3 hours with hourly changes. The material in butyl 
alcohol can be infiltrated with paraffin by adding melted 
