CUTTING AND SECTION-STRETCHING. 181 



right temperature is obtained by adjusting the distance of 

 the lamp. 



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 placed in the focus of a similar reflector. 



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. 



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

 position produces 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 perfectly flat even 

 when the same mass will only give rolled sections if cut dis- 

 connectedly. 



Special masses having less tendency to roll than pure 

 paraffin have been proposed. Thus a mass composed of four 

 parts of hard paraffin and one of vaselin has been recom- 

 mended. I recommend, however, that all such mixtures be 

 avoided. 



Mechanical means may be employed. The simplest of these 

 and perhaps the best 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 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 

 (MAYEE, ANDRES, and GIESBRECHT) ; Arch.f. mik. Anat., xxiii, 1884, p. 537 

 (DECKER) ; Bull. Soc. Beige Mic., x, 1883, p. 55 (FRANCOTTE) ; The Micro- 

 scope, February, 1884 (GAGE and SMITH) ; WHITMAN'S Meth.inMic.Anat., 

 1885, p. 91 ; Zeit.f. wiss. Mik., iv, 2, 1887, p. 218 (STRASSER) ; as well as 

 Journ. Roy. Mic. Soc., iii, pp. 450, 916, and other places. 



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



