CHAPTER VII 



THE GLYCERIN METHOD 



Mounting in glycerin, once a very popular method, has become al- 

 most obsolete. In its day, it was very good for unicellular and fila- 

 mentous forms and for various small objects; and we still use it for 

 moss protonema, which keeps the natural green and brown colors for 

 years. The transfer from glycerin to glycerin jelly is easy and safe, and 

 glycerin jelly has considerable consistency, so that it is easy to seal. 

 We ahnost never mount in glycerin, but transfer to glycerin jelly. The 

 glycerin method, except the final mounting, also constitutes the first 

 part of the Venetian turpentine method and, consequently, it is neces- 

 sary to learn the capabilities and limitations of glycerin. 



The method, from fixing to mounting, as used in connection with 

 staining and without staining, will now be described. 



Stained preparations. — The familiar Spirogyra is a good form to 

 begin with. Fix in chromo-acetic-osmic solution (| g. chromic, 3 c.c. 

 acetic acid, 6 c.c. 1 per cent osmic acid, and 90 c.c. water); or in a 

 chromo-acetic solution without osmic acid (1 g. chromic, 3 c.c. acetic 

 acid, and 96 c.c. water). Fix 24 or 48 hours and wash in running water 

 for 24 hours. At this point it is the usual practice to stain and transfer 

 to 10 per cent glycerin; but preparations are more nearly perfect if the 

 material receives more hardening than the chromic fixing agents can 

 give it, before it goes into the stain. Therefore, run it up, as if it were 

 to be imbedded in paraffin, until it reaches 85 per cent alcohol. The 

 following series is recommended: 2|, 5, 7|, 10, 15, 20, 30, 40, 50, 70, 

 and 85 per cent, with ^ hour in each of the first five grades; 2-4 hours 

 each in 20 and 30; 5 or 6 hours each in 40 and 50; all day or overnight 

 in 70 ; 24 hours in 85. The 85 per cent completes the hardening so that, 

 with reasonable care, the subsequent processes do little or no damage. 

 After the hardening in 85 per cent alcohol, run back to water through 

 the same series of alcohols, with one hour in each grade down to 30; 

 below 30, 20 minutes in each grade; water, 20 minutes, and then 

 stain. 



The most generally satisfactory stain is Haidenhain's iron-alum 

 haematoxylin. If there was any osmic acid in the fixing agent the 



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