IMBEDDING ME1HUDS (PAHAFFJN). 109 



will always cure rolling ! But it diminishes the tendency 

 to 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. For if a section has only a slight tendency to 

 curl, it will be held down flat by adhesion to the one 

 preceding it. 



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 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 (SCHTJLTZE) ; Mitth. Zool. Stat. Neapel, iv, 1883, p. 429 

 (MATEE, ANDEES, and GIESBBECHT) ; Arch.f. mik. Anat., xxiii, 1884, p. 537 

 (DECKEB) ; Bull. Soc. Bdg. Mic., x, 1883, p. 55 (FBANCOTTE) ; The Micro- 

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

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

 Mik., x, 2, 1893, p. 157, or Journ. Boy. Mic. Soc., 1894, p. 132 (Bosx) ; as 

 well as Journ. Roy. Mic. Soc., iii, pp. 450, 916, and other places. It must 

 be allowed that all these instruments are difficult to use, and that if they 

 are not perfectly adjusted they may easily injure the sections. And they 

 are less necessary than formerly, now that good processes for flattening out 

 sections have been worked out (see below, " Section-flattening," 138). 



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

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

 shape of a wedge five or six times as long as broad, the 

 object being contained in the broad part, and the edge 



