ANATOMICAL TECHNIQUE 459 



METHODS OF MOUNTING 



In the case of the great mass of vegetable tissues it is frequently 

 an advantage to bring about the sharpest possible accentuation 

 of the color contrasts resulting from staining by mounting in media 

 of high refractive index. For this purpose the sections must be 

 usually entirely freed from water. This end is effected by means 

 of absolute alcohol. The sections are transferred on a section- 

 lifter from the solution of safranin to a watch-glass of absolute 

 alcohol, excess of fluid having been removed by touching the lifter 

 to a piece of blotter or filter paper. From the first absolute 

 alcohol they are lifted to a second, which effects the final removal 

 of water. Too long immersion in the first absolute alcohol is 

 likely to extract too much of the safranin stain, but a longer stay 

 is advantageous if the sections have received an excessive colora- 

 tion in red. In case the sections have been cut from material 

 infiltrated with nitrocellulose, the latter may often be retained 

 with advantage. This object is attained by adding a little chlo- 

 roform to the two changes of absolute alcohol, this procedure hav- 

 ing the effect of preventing the softening of the nitrocellulose. 

 Should it appear desirable to remove the infiltrating substance 

 completely, the sections are transferred to ether after the second 

 absolute alcohol. In any case, after dehydration is effected 

 in any of the ways described, the sections are finally cleared 

 with a reagent of high refractive index. The most convenient 

 of these for vegetable preparations is chemically pure and an- 

 hydrous benzene or benzole. After clarification the preparations 

 are ready for mounting. This is effected in hard Canada balsam, 

 dissolved in whatever agent has been used to clear the sec- 

 tions. Benzole, xylol, chloroform, etc., are employed for this 

 purpose. 



The solution of balsam should not be too dilute, as the evapora- 

 tion of the solvent may under this condition result in the disas- 

 trous desiccation of the sections. Even where the section is not 

 actually left bare by the drying out of the mounting balsam, the 

 access of air is likely to promote a rapid fading of the colors. It is 

 usually necessary to flatten the sections because the balsam sets 

 by the evaporation of the solvent. This procedure is essential 



