124 METHODS OF MICROSCOPICAL RESEARCH. 



clears out the grooves on the top of the section 

 carrier with the back of a knife ; then he places his 

 specimen upon the machine, and paints it round 

 with gum solution, and the whole freezes fit for 

 cutting in one minute or so. With very little prac- 

 tice it is quite easy to cut fifty excellent sections of 

 each of fifteen or twenty specimens with one charge 

 of ice and salt. 



To manage Swift's knife, we proceed thus : 

 First take the blade away, and lay it flat upon a 

 smooth hone well oiled, and rub it first on one side, 

 then the other, until the entire edge on either side is 

 ground by the hone at once. The writer rubbed 

 over twenty hours before this was accomplished 

 with the razor blade of his Swift's knife. Both 

 sides of the blade are ground quite flat, to begin 

 with, not hollowed ; but cutlers either cannot or 

 will not grind a blade with its back and its edge 

 perfectly parallel, so that this has to be done by 

 one's self. Having ground the knife blade, we fix 

 it in the handle and strop it. We then take off the 

 handle and fix the blade in the carrier in such a 

 way that the edge must be perfectly level with the 

 top of the microtome, and on a much lower level 

 than the back. This position of the knife in the 

 frame is to the last degree essential, and we effect 

 it thus : First place the knife-blade in the frame, 

 and lower the screws which the edge of the blade 

 rests upon, so that the edge is lower than the back 

 a good deal. After making it firm, we complete the 

 levelling by freezing a piece of tissue, and taking 

 away a thick section, cutting away from us, with 

 the knife in the frame just as we have put it roughly. 

 We now place each end of the blade alternately 



