IMBEDDING METHODS. 93 



recent papers in Zeit. wiss. Mile, also that of Apathy, in the 

 paper quoted above (very complicated), and especially the 

 description of the two latest of Jung, viz. his model I and 

 model 11, by Mayer and Schoebel, in Zeit. iviss. Mik., xvi, 

 1899, p. 29 (see figure of model / in Jouni. Roy. Mic. Soc, 

 132, 1899, p. 546). Also Caepentee's The Microscope, 

 p. 463. 



146. Cutting and Section-stretching. — Paraffin sections are 

 cut dry, — that is, with a knife not moistened with alcohol or 

 other liquid. By this means better sections are obtained, but 

 a difficalty generally arises owing to the tendency of sections 

 so cut to curl up on the blade of the knife. It is sometimes 

 difficult by any means to unroll a thin section that has curled. 

 To prevent sections from rolling, the following points should 

 be attended to. 



First and foremost, the paraffin must not be too hard, 

 see § 151. 



If, after cutting has begun, the paraffin be found to be too hard, it 

 may be softened by placing a lamp near the imbedded object. But 

 then, the paraffin being warmed most on the side nearest the lamp, 

 becomes softer on that side, and the sections have a tendency to become 

 compressed and puckered-in on that side. 



If, on the contrary, the paraffin be found too soft, it may be hardened 

 by exposing it to the cooling influence of a lump of ice. 



It is often sufficient to moderate the temperature of the room by 

 opening or closing the window, stining the fire, setting up a screen, or 

 the like. 



For other devices for warming or cooling the paraffin see Held, Arch. 

 Anat. Phys., Anat. Ahth., 1897, p. 315; van Walsem, Zeit. wiss. Mih., 

 xi, 1894, p. 218; Lbndenfeld, ibid., xviii, 1901, p. 18; Keause, ibid., 

 XXV, 1908, p. 299 ; Foot and Steobell, Biol.. Bull. Wood's Hole, ix, 1905, 

 p. 281. 



Secondly, the knife should be set square, for the oblique 

 position encourages rolling, and the more the knife is oblique 

 the more do the sections roll. 



Thirdly, it is better to cut ribbons than disconnected sec- 

 tions ; ribbons of sections will often cut flat, when the same 

 mass will only give rolled sections if cut disconnectedly. 



Rolling may often be lessened or suppressed by cutting 

 the sections thinner, 



