Reagents 35 



the J, use equal parts of the J and absolute alcohol; for the J, use 

 equal parts of the J and absolute, and for the T \ , equal parts of the 

 and absolute. The f can be guessed at with sufficient accuracy. 

 About 4 hours in each grade is long enough; change morning, 

 noon, and night. The pure xylol should be changed once or twice. 

 While the pure xylol must not be used again for this purpose, it is 

 still good for dissolving paraffin ribbons when staining on the 

 slide. 



Xylol is the best agent for clearing sections just before mounting 

 in balsam. Preparations cleared in xylol harden more rapidly, 

 and this is such a decided advantage that even when sections have 

 been cleared in cedar oil or clove oil it is worth while to give them a 

 minute or two in xylol before mounting. 



Xylol evaporates so rapidly that one must take care not to let 

 sections become dry before applying the balsam. Thin sections 

 perfectly dehydrated will clear in a few seconds; a minute or two 

 should be sufficient for sections 20 (JL in thickness. If there is much 

 moisture in the air, or if the absolute alcohol is not above suspicion, 

 clear sections in clove oil before transferring to xylol. 



Chloroform. Some botanists use chloroform to precede the 

 infiltration 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 entitles 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 slightly 

 amber tint, the color resembling a weak clove oil. It should have 

 the pleasant oclor of cedar wood. The very expensive cedar oil 

 used with immersion lenses is not needed for clearing or for preced- 

 ing infiltration with paraffin. It is claimed that material cleared in 

 cedar oil does not become so brittle as that cleared in xylol or chloro- 

 form. 



Clove Oil. This is an excellent agent for clearing sections and 

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



