IMBEDDING METHODS (PARAFFIN). 117 



of commercial paraffin as giving a mass particularly favour- 

 able 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 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. The object of this preparation is to make the 

 mass stickier, in view of cutting ribbons. 



For mixtures of paraffin with other substances, none of which I consider 

 to offer any advantage, see previous editions. 



143. Soap Masses. These have never been much used, and are now en- 

 tirely discarded in favour of paraffin. But see previous editions, or the papers 

 of POLZAM (MorpTi. Jahrb., iii, 1877, 3tes Heft, p. 558, from Salensky's 

 paper on the gemmation of Salpa, loc. cit.) ; KADYI (Zool. Anz., 37, 1879, 

 vol. ii, p. 477) ; DOLLKEN (Zeit.f. wiss. Mik., xiv, 1, 1897, p. 32). 



Gelatin Masses. 



144. Gelatin Imbedding is a method that has the advantage 

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

 degree dehydrated, and may render great service in the 

 study of very watery objects. 



The modus operandi is, on the whole, the same as for other 

 fusion masses, with the difference that the objects are pre- 

 pared by saturation with water instead of alcohol or a clearing 

 agent. After the cooling of the mass it may sometimes be 

 cut at once, but it is generally necessary to harden it. This 

 may be done by treatment for a few minutes with absolute 

 alcohol (KAISER), or for a few days with 90 per cent, alcohol 

 (KLEBS) or chromic acid (KLEES) or formaldehyde (Ni COLAS), 

 or it may be frozen (SoiLAs). 



The mass is removed from the sections by means of warm 

 water. 



MAYEB (Mitth. Zool StaL Neapel, ii, 1880, p. 27) for coarse researches 

 leaves the mass in the sections (if the tissues have been stained previously) 

 as it becomes sufficiently transparent in balsam. He recommends as a 



