PKEPARED PARAFFIN. 187 



chains or ribbons,, collodionising them if necessary. Fix 

 them in serial order on a slide according to one of the methods 

 given in Chap. XVII. Warm, and remove the paraffin with 

 naphtha. Stain or mount. 



Paraffin Masses. 



285. Pure Paraffin. It is now pretty generally admitted 

 that pure paraffin forms an imbedding mass greatly superior 

 for ordinary work to any of the many fatty mixtures that used 

 to be recommended. I have only to repeat here that a 

 paraffin melting at 45 C. is that which in my experience gives 

 the best results so long as the temperature of the laboratory is 

 between 15 and 17 C.; whilst for a temperature of 22 C. a 

 paraffin melting at 48 is required. If the temperature of 

 your laboratory have risen much above 22 C. you had better 

 give it up, for good section-cutting with paraffin under such 

 conditions is next to impossible. 



Paraffin of the melting-points named is easily found in 

 commerce. Intermediate sorts may be made by mixing hard 

 and soft paraffin. Two parts of paraffin melting at 50 

 with one of paraffin melting at 36 C. give a mass melting 

 at 48 C. 



Many workers of undoubted competence prefer masses 

 somewhat harder than those recommended, viz. of melting- 

 points varying between 50 and 55 C. for the normal tem- 

 perature of the laboratory. Some authors still recommend 

 masses melting at 60 C. or higher. I can only repeat that I 

 am convinced that, besides being most hurtful to tissues, such 

 masses have no raison d'etre whatever in temperate climates. 



Paraffin had better be obtained from Griibler, or one of the 

 known dealers in microscopic reagents. Gaule recommends 

 that the bluish transparent sorts be taken. I should say, 

 transparent by all means, but, if possible, rosy rather than 

 bluish. New paraffin is bluish ; if kept long, which is well, 

 it generally becomes rosy. 



286. Prepared Paraffin (Pure) . GRAF SPEE (Zeit.f. wiss. MiL, 

 ii, 1885, p. 8) recommends the following preparation of com- 

 mercial paraffin as giving a mass particularly favorable for 

 ribbon- section cutting. Paraffin of about 50 C. melting- 

 point is taken and heated in a porcelain capsule by means of 



