REAGENTS 39 



sam. If there is much moisture in the air, or if the absohite alcohol is not 

 above suspicion, clear sections in clove oil before transferring to xylol. 



Chloroform. — Some botanists use chloroform to precede the infiltra- 

 tion with paraffin. In the later stages of infiltration it is more easily 

 removed than xylol. It seems to possess no other advantages, and for 

 clearing sections just before mounting in balsam it is inferior to xylol 

 or clove oil. Its value in hardening celloidin and as a fixing agent en- 

 titles it to a place in the histological laboratory. 



Cedar oil. — It is not always easy to get good cedar oil. If the stuff 

 offered for sale looks like turpentine and smells like it, it is worthless 

 for histological purposes. Good cedar oil has a shghtly amber tint, the 

 color resembling a weak clove oil. It should have the pleasant odor of 

 cedar wood. The very expensive cedar oil used with immersion lenses 

 is not needed for clearing or for preceding infiltration with paraffin. It 

 is claimed that material cleared in cedar oil does not become so brittle 

 as that cleared in xylol or chloroform. 



Dr. E. J. Kraus has used cedar oil extensively in clearing large ob- 

 jects — strawberries and gooseberries either whole or cut in two, sec- 

 tions of apple 2 to 4 mm. thick, and similar objects. This method is 

 proving valuable in vascular anatomy, some material showing the 

 course of bundles very clearly in pieces so large as centimeter cubes. 



Xylol can be used in the same way, but is so volatile that specimens 

 often dry up. Dr. Land suggests equal parts of xylol and carbon disul- 

 phide for clearing large objects which are to be examined without sec- 

 tioning. 



Clove oil. — This is an excellent agent for clearing sections and small 

 objects just before mounting in balsam. It clears more readily than 

 xylol. When the absolute alcohol has deteriorated so that xylol no 

 longer clears the sections, clove oil may still clear with ease. While clove 

 oil will clear from 95 per cent alcohol, it is better to use absolute. Since 

 preparations cleared in clove oil harden slowly, it is a good plan to 

 treat them with xylol before mounting in balsam. Gentian violet is 

 somewhat soluble in clove oil, and this fact makes it possible to secure 

 a beautiful differentiation, because the stain is extracted from some 

 elements more rapidly than from others. The stain may be extracted 

 completely from the chromosomes during the metaphase and still 

 remain bright in the achromatic structures. After the desired differen- 

 tiation has been attained, the preparation should be placed in xylol to 

 remove the clove oil, since the continued action of the clove oil would 



