120 The Microscope. 



The study need not be confined to leaves, as the flowers 

 may also be subjected to the same operation, and the mode of circu- 

 lation be observed even in the organs of reproduction. In the leaves the 

 stronger and more prominent veins do not take up the color readily 

 while the plant is living, but the finer veins and cellular tissues are 

 readily colored. 



These coloring fluids may be injected into the stem of the rooted 

 plant, but greater care and patience are necessary than by the 

 methods of cuttings. — American Monthly Microscopical Journal. 



Section Fixatives. — Of the three fixatives now in general use — 

 shellac, collodion and albumen — shellac is considered the best for 

 objects colored, in toto. The carbolic- acid shellac introduced by 

 Mayer has been found to be unreliable in some respects. Carbolic 

 acid warm is injurious to some tissues, e. g., the dermis of verte- 

 brates. The alcoholic solution is a perfectly harmless fixative. The 

 method of using, which differs in important points from the one 

 prescribed by Giesbrecht, is as follows : 



A. The object slide, heated to about 50° C, is coated with 

 shellac in the usual manner, by drawing a glass rod wet with the 

 solution once or twice over its surface. As soon as the slide is cool 

 and the film of shellac hard and no longer sticky, the sections are 

 arranged dry, and then gently pressed down by means of an elastic 

 spatula (horn or metal) until they lie flat and smooth on the slide. 



B. Expose the slide thus prepared to the vapor of the ether. 

 For this purpose the slide may be placed in a glass cylinder of 

 suitable size and closely stoppered. The cylinder is placed in a hori- 

 zontal position, or, at least, so inclined that the slide lies wholly 

 above the ether. The saturation of the sections will be sufficiently 

 complete in about half a minute. 



C. The slide is next to be warmed in the water-bath in order 

 to evaporate the ether. The paraffin is then removed and the 

 mounting completed in the usual manner. 



It is best to use balsam dissolved in turpentine or benzole,^ 

 rather than in chloroform, as the latter softens the shellac, and thus 

 often loosens the sections. 



One advantage of this method of using shellac is that it permits 

 of arranging and flattening the sections on the slide. Ordinarily, 

 sections are placed while the adhesive coating is soft, and must then 

 lie as they fall. With reference to collodion, Mayer remarks that it 

 depends entirely upon the quality of the gun-cotton employed 

 whether the section bear well treatment with alcohol and aqueous 



