92 IMBEDDING METHODS. 



such as the Cambridge, the Minot, or the Reinhold-Giltay, will give 

 good results with much harder paraffin, and, in fact, require such. 



Stout knives of hard steel will take a harder paraffin than thin 

 ones of soft steel ; but the latter may be preferable for soft masses. 



For thin sections a harder paraffin is required than for thick ones. 



Hard objects require a harder paraffin than soft ones. 



BRASS (Zeit. iviss. Mik., ii, 1885, p. 300) recommends paraffin that 

 lias been kept for some years, as it has less tendency to crystallise 

 than new paraffin. 



Paraffin of various melting-points is easily found in commerce. 

 Intermediate sorts may be made by mixing hard and soft paraffin. 

 I find that 2 parts of paraffin melting at 50 with 1 of paraffin 

 melting at 36 C. give a mass melting at 48 C., and a mixture of 1 

 part of that melting at 53 with 1 part of that melting at 45 gives a 

 mass melting at 50 C. 



According to E. BURCHARDT (Jena Zeit. Natunc., xxxiv, 1900, 

 p. 719) mixtures of paraffins of different melting-points give better 

 results than an unmixed paraffin of the same melting-point as the 

 mixture. He recommends 10 parts of 40 paraffin + 1 of 45 -f 1 

 of 52 + 1 of 58 + 6 of 60. 



For methods for ascertaining melting-points see Kissling, Chem. 

 Centralb. ii, 1901, p. 507. 



152. Overheated Paraffin. SPEE (Zeit. wiss. Mik., ii, 1885, p. 8) takes 

 paraffin of about 50 C. melting-point and heats it in a porcelain capsule 

 by means of a lamp until it has become brownish-yellow, and after 

 cooling shows an unctuous or soapy surface on being cut. This mass 

 may be obtained ready prepared from Griibler. The object of this 

 preparation is to make the mass stickier, in view of cutting ribbons. 



VAN WALSEM (Verh. Akad. Wetensch. Amsterdam, 1899, p. 132) still 

 recommends the addition of 5 per cent, of yellow wax to paraffin of 52 

 to 57 melting-point (for large sections of central nervous system). 



JOHNSTON (Journ. Appl. Micr., vi, 1903, p. 2662) adds 1 per cent, of 

 india-rubber in very small pieces, dissolved by heating to 100 C. for 

 twenty-four hours, or several days to 60 C. Clear with xylol. For 

 very brittle objects. 



153. Soap Masses, These have never been much used, and are now 

 entirely discarded. But see early editions, or POLZAM (Morpli. Jahrb., 

 iii, 1877, p. 558) ; KADYI (Zool. Anz., 1879, vol. ii, p. 477) ; DOLLKEN 

 (Zeit. wiss. Mik., xiv, 1897, p. 32). 



Gelatin Masses. 



154. Gelatin Imbedding is a method that has the advantage of 

 being applicable to tissues that have not been in the least degree 

 dehydrated. 



