162 PREPARATION AND MOUNTING 



which are found in rhubarb are wanted, some parts con- 

 taining these are chosen and left in a small quantity of 

 water until the mass becomes soft, and this is more quickly 

 effected when the water is not changed. The mass must be 

 then placed upon a glass plate when practicable, or in the 

 trough when large, and with the aid of two needles the 

 matter may be removed from the spiral vessels, which are 

 plainly seen with a comparatively low power ; and by con- 

 veying these to a clean slip of glass, repeating the process, 

 and at last washing well, good specimens may be procured. 

 Most of these should be mounted in some of the preservative 

 liquids in the manner described in Chapter V. Many, 

 however, may be dried on the slide, immersed in turpentine, 

 and then mounted in balsam ; but liquid is preferable, as it 

 best preserves their natural appearance. Certain kinds of 

 vegetables require a different treatment to separate these 

 spiral vessels. Asparagus is composed of very hard vegetable 

 matter, and some have recommended the stems to be first 

 boiled, which will soften them to such a degree that they 

 may easily be separated. Dilute acids are also occasionally 

 used to effect this ; and in some instances to obtain the 

 raphides caustic potash may be employed ; but after any of 

 these agents have been used, the objects must be thoroughly 

 cleansed with water, else the dissecting instruments (and 

 perhaps the cell) will be injured by the action of the re- 

 maining portion of the softening agent. 



For the dissection of animal tissues it is necessary that 

 the instruments be in the best order as to sharpness, &c. ; 

 and as the rules to be observed must necessarily be some- 

 what alike in many instances, the treatment required by 

 some of the objects most frequently mounted will now be 

 described. We may here remark that cartilage can be 

 best examined by taking sections which will show the ar- 

 rangement of the cells very perfectly. This, however, is 

 plainly seen in the mouse's ear without any section being 

 necessary. Glycerine, the preservative liquids before men- 

 tioned, and Canada balsam are all used to mount it 



