188 IMBEDDING METHODS. 



a spirit lamp. After a time disagreeable white vapours are 

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

 at in from one to six hours, according to the quality of the 

 paraffin. The mass then becomes brownish yellow, and after 

 cooling shows an unctuous or soapy surface on being cut. 

 The melting-point will be found to have risen several degrees. 

 This mass may be obtained ready prepared from Griibler. 



BRASS (loc. cit., p. 300) recommends the use of paraffin that 

 has been kept for some years, as such has, less tendency to 

 crystallise than new paraffin. In this I concur. 



FOETTINGEK recommends (Arch, de Biol., vi, 1885, p. 124) a somewhat 

 complicated treatment with caustic potash, in which I have no faith (it was 

 tried by one of the writers of the Traite des Meth. techn., during the pre- 

 paration of that work). 



287. Paraffin Mixtures and other Similar Masses. Of these 

 the only ones that I think can be recommended for a moment 

 are the following : SCHULGIN'S paraffin with a little cerisin 

 (this is evidently what Schulgin means by "ceresin"). Or, 

 instead of cerisin, white wax (see Zool. Anz., 1883, p. 21); 

 or the mixture of BRASS (Zeit. f. wiss. Mik., ii, 1885, p. 301), 

 who recommends four to six parts of white wax to 100 of 

 paraffin. Sections may be cleared with benzin. 



Cacao Butter, pure, is still used by some histologists. It melts some- 

 what under 35 C. The objects may be prepared by penetration with clove 

 oil, which may also be used for removing the mass from the sections. 



Bayberry Tallow (Myrtle Wax, Vegetable Wax, Japan Wax). 



See Journ. Roy. Mic. Soc., 1885, p. 735 ; ibid., 1888, p. 151 ; MILLER and 

 BLACZBUEN, New York Med. Eec., 1885, p. 429 ; Amer. Mon. Mic. Journ., 

 1887, p. 164 ; Journ. Roy. Mic. Soc., 1887, p. 1048 ; FBANCOTTE, Bull. Soc. 

 Beige de Mic., 1887, p. 140 ; Zeit.f. wiss. Mik., iv, 2, 1887, p. 230 ; Journ. 

 Roy. Mic. Soc., 1887, p. 681. Bayberry tallow has the, for some objects, 

 valuable quality of working with alcohol as a solvent instead of such solvents 

 as chloroform or benzol, which undoubtedly alter certain tissues more than 

 alcohol. But for general work it has not succeeded in taking the place of 





Soap Masses. 



288. Utility of Soap Masses. Soap masses certainly have 

 many good points. The solvent is alcohol ; the mass is highly 

 transparent, very penetrating, and a good mass cuts far better 

 than even paraffin. The mass may be cut either dry or with 



