vni PRACTICAL DIRECTIONS 139 



middle, is not more than J inch square. Hold the cork 

 firmly in the left hand, with the wrist resting on the table, 

 and with a razor cut the thinnest possible slices of the 

 paraffin block, including the imbedded object. The razor 

 must be held firmly grasped at the junction of blade and 

 handle, and kept with the surface of the blade parallel with 

 that of the block : use almost the whole length of the edge 

 for each section. With a little practice you will be able to 

 cut sections so thin as to be quite transparent under the 

 high power. 1 



/. Clearing and mounting. Place the section on a slide 

 and warm it gently on the water-bath until the paraffin 

 melts, and then add a large drop of turpentine or xylol in 

 order to dissolve the paraffin. Then draw off the turpentine 

 with blotting-paper and replace it by a fresh drop, repeating 

 the process until all the paraffin is dissolved : put on a 

 cover-glass and Examine. 



If you wish to be sure that the parts of your sections are 

 not displaced in mounting, or to mount several sections on 

 one slide, the latter should first be smeared over with a very 

 thin layer of a mixture of collodion and oil of cloves, or of 

 glycerine and white of egg, in equal parts : then place the 

 sections on the slide, warm, and immerse the whole slide in 

 a small vessel of turpentine or xylol, leaving it until all the 

 paraffin is dissolved. 



In order to make a permanent preparation, -remove the 

 paraffin with turpentine or xylol, as above, draw off the 

 turpentine, place a drop of Canada balsam on a cover- 

 glass and very gently lower the cover-glass on the object, 

 spreading out the balsam in a thin, even layer. Before 

 long, the balsam will have set quite hard, and the sections 

 may be preserved for an indefinite period : the balsam will 

 set more quickly if you leave your preparations over the 

 water-bath for a short time. 



Remember that object, razor, slide, and cover must be 

 kept free from water, the presence of which, from the stage 

 of dehydration onwards, is fatal to success. 



Examination of Compound Tissues. 



Examine the following sections, prepared as described 

 above, first with the low, and then with the high power, 



1 If you are working in a properly furnished laboratory you will 

 probably learn how to cut sections with a microtome, or section- 

 cutting machine, which gives much better results and is absolutely 

 necessary when a complete series of sections of the same object 

 is required. 



