CHAPTER VIII. 8 7 



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, stirring the fire, setting up a screen, or 

 the like. 



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

 Anat. Phys., Anat. AUh., 1897, p. 345 ; VAN WALSEM, Zeit. wise. Mik., 

 xi, 1894, p. 218 ; LENDENFELD, ibid., xviii, 1901, p. 18 ; KRAUSE, ibid., 

 xxv, 1908, p. 299 ; FOOT and STROBELL, 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 sections ; 

 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. 



Mechanical means may be employed. The simplest of these is as 

 follows : 



During the cutting the edge of the section that begins to curl is 

 caught and held down on the blade of the knife by means of a small 

 camel-hair brush with a flat point, or by a small spatula made by 

 running a piece of paper on to the back of a scalpel. Or, which is 

 much better, the section is held down by means of an instrument 

 called a " section-stretcher." This consists essentially of a little 

 metallic roller suspended over the object to be cut in such a way as 

 to rest on its free surface with a pressure that can be delicately 

 regulated so as to be sufficient to keep the section flat without in any 

 way hindering the knife from gliding beneath it. 



See the descriptions of various forms of section-stretchers, Zool. 

 Anzeig., vol. vi, 1883, p. 100 (SCHULTZE) ; Mitth. Zool. Stat. Neapel, iv, 

 1883, p. 429 (MAYER, ANDRES, and GIESBRECHT) ; Arch. m,\k. Anat., 

 xxiii, 1884, p. 537 (DECKER) ; Bull. Soc. Belg. Mic., x, 1883, p. 55 (FRAN- 

 COTTE) ; The Microscope, February, 1884 (GAGE and SMITH) ; WHIT- 

 MAN'S Meth. in Mic. Anat., 1885, p. 91 ; Zeit. wiss. Mik., iv, 1887, p. 2 

 (STRASSER) ; ibid., x, 1893, p. 157 (BORN). The best are those 

 and Born. 



I find that MAYER'S, beautifully made by JUNG, works admirably 

 and is most valuable. 



Another plan is to allow the sections to roll, but to contn 

 rolling. To this end, the block of paraffin is pared to the shape of a 



