IMBEDDING METHODS. \i\\ 



these are seldom realised in the British Isles, and, whilst I 

 quite admit that such hard paraffin may have its raison 

 d'etre for Naples, I hold that for that very reason it is 

 in general unnecessarily hard for cooler climates. 



My recommendation of a relatively soft paraffin refers l<> 

 work with the Thoma sliding microtome. Microtomes with 

 fixed, knives, 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 tlian 

 thin ones of soft steel ; but the latter may be preferable I'm- 

 soft masses. 



For thin sections a harder paraffin is required than I'm- 

 thick ones. 



Hard objects require a harder paraffin than soft ones. 



BKASS (Zeit. wiss. Mik., ii, 1885 ; p. 300) recommends 

 paraffin that has been kept for some years, as it lias 

 less tendency to crystallise than new paraffin. 



Paraffin of various melting-points is easily found in com- 

 merce. Intermediate sorts may be made by mixing hard 

 and soft paraffin. I find that two parts of paraffin nieltiiiLr 

 at 50 with one of paraffin melting at 36 C. give a in;, 

 melting at 48 C., and a mixture of one part of that melting 

 at 53 with one part of that melting at 45 gives a mas 

 melting at 50 C. 



According to E. BURCHAEDT (Jena Zc-it. Nattinr., .\xxiv, 

 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 pan- of 

 40 paraffin + 1 of 45 + 1 of 52 + 1 of 58 + l> of r,D. 



For methods for ascertaining melting-points see A'/V 

 Chem. Centralb. ii, 1901, p. 507. 



152. Overheated Paraffin. SPEE (Zeit. wiss.Mik.,ii, lS-->. p. M takes 

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

 by means of a lamp until it has become brownish -\<-ll>\v. ;m<l ;ii'1 

 cooling shows an unctuous or soapy surface on beiii,^ cut. 

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

 paration is to make the mass stickier, in viV\v of culling ribbons. 



YAN WALSEM (Verh. Akad. Wetcnsch. Amsterdam. I- p. 

 recommends the addition of 5 per cent, of yellow wax to para din 

 to 57 melting-point (for large sections of central aervous sys 



JOHNSTON (Journ. Appl, Micr., vi, 1903, p. '2W2) adds 1 per cent, of 



