CUTTING AND SECTION-STRETCHING. 147 



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

 must be taken of a melting point suitable to the temperature 

 of the laboratory (for the winter season the temperature of 

 the laboratory being between 15 and 17 C., a paraffin 

 melting at about 45 C. should be taken; for hot summer 

 weather, laboratory at 22 C., a paraffin of 48 C. melting 

 point) . 



The exact degree of hardness necessary must be determined 

 by experiment. If, after cutting has begun, the paraffin be 

 found to be too hard, it may be softened by the following 

 simple expedient (FoL, Lehrbuch d.vergl. mikr. Anat.jip. 123) : 

 A lamp provided with a parabolic reflector is set up near the 

 microtome in such a position that the heat-rays of the flame 

 are thrown by the reflector on to the imbedded object. The 

 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 



