Io2 IMBEDDING METHODS. 



Paraffin Masses. 



278. 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 tempera- 

 ture 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 and go dredging, for good section 

 cutting with paraffin under such conditions is next to im- 

 possible. 



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 recommend masses melting at 60 C. or 

 higher. 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. 



279. Prepared Paraffin (Pure). GRAF SPEE (Zeit.f. wiss. Mils., 

 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 

 a spirit lamp. After a time, disagreeable white vapours are 

 given off, and the mass shrinks a little. This result is 



