40 METHODS IN PLANT HISTOLOGY 



cause the preparation to fade. Do not use a Stender dish for clove oil, 

 but keep it in a 50 c.c. bottle. Put on a few drops, and immediately 

 drain them off in such a way as to remove the alcohol as completely as 

 possible. Then flood the slide and pour the clove oil back into the 

 bottle, repeating the process until the proper differentiation has been 

 reached. Replace the clove oil with xylol and mount in balsam. With 

 stains not soluble in clove oil, the xylol is not necessary, except to facil- 

 itate the hardening of the preparation. 



Clove oil may be used in removing the celloidin matrix from celloidin 

 sections. It is useless as an agent to precede infiltration with paraffin. 



Eycleshymer's clearing fluid. — This is a mixture of equal parts of 

 bergamot oil, cedar oil, and carboHc acid. It clears readily from 95 per 

 cent alcohol, and consequently is useftd in clearing celloidin sections 

 when it is desirable to preserve the celloidin matrix. In sections 

 stained with haematoxyhn, or haematoxylin and eosin, the stain may 

 be removed completely from the matrix by the use of acid alcohol, 

 and the matrix may be preserved by clearing from 95 per cent alcohol. 



It is not intended that the mixture should be used to precede infiltra- 

 tion with paraffin. 



Other clearing agents. — Bergamot oil, carbohc acid, turpentine, 

 benzine, gasohne, and other reagents have been tried for clearing, 

 but none seem to be worth more than a warning mention. 



MISCELLANEOUS REAGENTS 



Canada balsam is used almost exclusively for mounting. Very thick 

 balsam is disagreeable to handle and makes unsatisfactory mounts. 

 Very thin balsam, in drying out, allows bubbles to run under the cover. 

 Xylol is cheaper than balsam, and consequently the balsam on the 

 market is likely to be too thin for immediate use. The stopper may be 

 left out until the balsam acquires the proper consistency. Balsam 

 must not be acid. If there is the sUghtest acid reaction, most stains 



will fade. 



Paraffin should be of at least two grades, a soft paraffin melting at 

 40° to 45° C, and a hard paraffin melting at 52° to 54° C. Grubler's 

 paraffin and most imported paraffins melt at the temperature indicated 

 on the wrappers. The melting-point indicated on the wrappers of 

 paraffins sold by some American dealers does not enable one to make 

 even a guess as to the real melting-point. Paraffin marked 70° C. may 

 melt at 60° C, and other grades are hkely to melt before the tempera- 



