U6 CHAPTER VIII. 



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; and others recommend masses 

 melting at 60 C. or higher. 



So, for instance, Heidenhain (58), Apathy (55), Eabl 

 (56), Mayer (58 to 60 in summer; in winter about 56, 

 but never less than 50). Mayer points out (Gruiidziige, 

 p. 90) that at Naples the temperature during five months of 

 the summer and autumn is over 22 C. in the laboratory, 

 sometimes over 30. Temperatures such as these are seldom 

 realised in the British Isles, and whilst I quite admit that 

 the hard paraffin employed by Mayer may have its raison 

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

 general unnecessarily hard for cooler climates. 



For thin sections a harder paraffin is required than for 

 thick ones ; and the thinner the sections, the harder should 

 the paraffin be. 



The figures above given have been repeatedly verified and 

 are undoubtedly correct. But an important explanation 

 remains to be made. The statements refei* to work with the 

 Thoma sliding microtome. I have since ascertained that 

 microtomes with fixed knives, such as the Cambridge, the 

 Minot, or the Reinhold-Giltay, will give good results, so far 

 as cutting is concerned, with much harder paraffin, and, in 

 fact, require such. This is an advantage, so far as the 

 obtaining of very thin sections is concerned ; but it seems 

 to me to remain true that for delicate work it is well in the 

 interest of the preservation of the tissues to use a paraffin of 

 as low a melting-point as possible. 



Paraffin had better be obtained from Griibler, or one of 

 the known dealers in microscopic reagents. BRASS (Zeit. f. 

 wiss. Mik., ii, 1885, p. 300) recommends such as has been 

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

 than new paraffin. 



124. Prepared Paraffin (Pure). G-RAF SPEE (Zeit. f. wiss. 

 Milf., ii, 1885, p. 8) recommends the following preparation 



