MOUNTING 



ether, chloroform, absolute alcohol, \\lol, benzene, ;m<l essential oils. 



Since these must be employed in both paraffin and crlloidin embeddm-, 

 fat cannot be very satisfactorily demons! rated by the.-e technics. Kro/.en 

 sections (made with a free/ing mierotoine) of fn-h or I'ormalin-ti \ed 

 tissues are therefore preferable (in some instances indispensable) ; i|],. s ,. 

 may be satisfactorily stained \viih Sudan JI1 (red), Sharlach |{ (red), 

 Nile blue (blue); they must be mounted in glycerin jellv. 



Osniic acid, however, renders certain fats resistant !o solution in 

 oils, and tissue so fixed may accordingly be treated by the pa ratlin teeh- 

 nic; but thick cedar oil must be substituted for xylol or chloroform, and 

 absolute alcohol should be avoided : 



1. Fix small pieces of fatty tissue in Flemming's fluid for two days. 



2. (a) Embed in paraffin (use cedar oil), section, and mount in 



euparal; or 

 (b) Embed in celloidin, the different solutions of which should 



be made up in 95 per cent, alcohol (see Kingsbury, Anat. Rec., 



5, 6, 1911). 



Technic for Demonstrating Chromaffin Granules. Chromaifm 

 material ('pheochrome' granules ; aclrenin granules) is highlv susceptible 

 to solution by acids. When preserved the chroniaffin granules react to 

 chromium (acid and solutions of salts) and stain light brown. The 

 best method for their preservation is Kelly's fluid (see page 728), which 

 comcidently stains the granules. Paraffin or celloidiu sections may be 

 stained with various nuclear dyes for the clear differentiation of the 

 nuclei. 



MOUNTING 



After staining, the sections are opaque; they must be rendered 

 transparent for microscopic examination. This is accomplished by per- 

 meating the sections with oil; but since oil and water are not miscible, 

 the tissue must first be thoroughly dehydrated with alcohol. Immers- 

 ing thin sections in 95 per cent, alcohol for three to fi\e minutes is 

 usually sufficient for this purpose unless xylol is to be used as the clarify- 

 ing oil or unless the stain is injured by so prolonged an immersion. 

 In either of these cases absolute alcohol is to be used for dehydration, 

 because of its more rapid and thorough action. 



Clarification. Sections, cither free or fastened to the slide, an- 

 immersed in oil until clear. Free sections will at first float on the oil, 

 but when fully permeated will sink. Attached sections should lose all 



