252 Modern Microscopy 



With the Cambridge ' rocker ' and similar microtomes 

 an ordinary razor is generally used ; it should not be 

 too much hollow - ground, and its cutting edge should 

 be straight, not curved, as in the generality of English 

 razors. If much work is intended, it is well to have more 

 than one knife of the required pattern, so that, should 

 the edge of one be accidentally turned, another may be 

 in readiness, and work proceeded with without delay for 

 sharpening. 



Sharpening Knives. To a beginner in microtomy, the 

 one great bugbear is the sharpening of the knives. The 

 keenness of the knife-edge is of pre-eminent importance, 

 and the sooner the beginner realizes the fact that for the 

 production of good work the knife-edge must be absolutely 

 perfect, the earlier will one of his great troubles in micro- 

 tomy be over. 



One way out of the difficulty is to send the knife to an 

 instrument-maker, if one can be found that understands 

 the business. The ordinary tradesman sharpens a razor 

 well, but is quite incapable of imparting the requisite keen- 

 ness to a microtome knife unless specially trained. The 

 right kind of microtomist will wish to learn the method of 

 sharpening his knives, and thus be independent of the 

 professional knife-grinder. Practice alone can bring per- 

 fection in this art ; we will, however, attempt to smooth 

 the path. 



It is impossible to hold the knife during the sharpening 

 at the correct angle without the aid of an appliance. 

 Luckily, this is simple enough, and consists merely of a 

 piece of steel bent to fit over the back of the knife. This 

 slides on the knife, and is tightened up by means of a thumb- 

 screw. Several forms are made, but this one answers 

 the purpose extremely well ; it is very strong, cannot 

 shift its position when in use, and is cheap. In use it raises 

 the back of the knife the requisite amount to give the edge 

 the right bevel. Each knife should have its own blade- 

 holder kept solely for its own use. The various sectional 



