Accessory Apparatus 255 



the knife. This is the so-called wire edge, and may be 

 removed by grinding in the opposite direction, plane side 

 downwards. Very slight pressure must be used in honing, 

 the weight of the knife and the suctorial action of the 

 lubricant being sufficient in the case of the larger knives. 

 Patience and delicacy of touch are the factors in success. 

 If the honing has been successfully accomplished, the 

 edge under the microscope should present a straight un- 

 broken line, perhaps very slightly serrated, but with 

 nothing in the nature of a decided notch. The serrations 

 must be removed by stropping. 



The Strop. — The strop for microtome knives is obtained 

 from Walb, and the size recommended is 36 centimetres 

 long. It is made by securing a strip of Eussia leather 

 to a firm convex base; this is then fixed at each end 

 to a stout wooden bow, the resulting stropping surface 

 being convex and yielding very slightly to pressure. 

 These strops are sent out by the maker with a thick 

 coating of red paste upon the surface. The writer 

 has never been able to get good results by using 

 the strop in this condition. It may be that others are 

 more successful with paste-covered strops, and one would 

 naturally infer that so excellent a mechanic as Herr Walb 

 would send out his strops in the very finest condition for 

 microtome knives, especially so as the strops are made ex- 

 pressly for these knives. The practice of the writer, however, 

 is to get rid of the red paste in the following manner : The 

 stropping surface first receives a coat or two of sperm-oil ; 

 after this has been absorbed the strop is very carefully 

 scraped or shaved with a keen razor — great care must be 

 taken not to cut the strop. In this manner the major 

 portion of the red paste is removed. Then, by applica- 

 tion of sperm-oil and rubbing with a cloth, more of the 

 paste is removed from the grain of the leather. Subse- 

 quently the strop receives a coat of sperm-oil, and is placed 

 for a few days in a warm, dry place. The oil causes the 

 red paste to work to the surface, from which it is scraped 



