16 



STUDENTS HISTOLOGY 



SHARPENING KNIVES 



In the majority of instances of failure to produce suitable sec- 

 tions for microscopical work, the cause can be set down to dull 

 knives, and we would urge the student to practice honing until able 

 to put cutting instruments in good condition. If he will but start 

 properly, success is sure. Nine -tenths of the microtomes are pur- 

 chased because of failure in free-hand work with a dull knife ; but 

 no advantage will ~be gained by a machine, if the student be incapa- 

 ble of keeping the knife up to a proper degree of keenness. 



A knife is a wedge, and for our purpose the edge must be of 

 more than microscopical tenuity it being impossible with the 

 microscope to discover notches and nicks if properly sharpened. 



It is impossible to secure the best results with indifferent tools. 



FIGS. 10 AND 11. METHOD OF HONING. 



The knife is first brought with its heel in the position shown at A, Fig. 10. It is then drawn 

 forward as indicated by the curved dotted line until, at the end of the stroke, the position C 

 is attained. Fig. 11 indicates the method of turning the blade before reversing and between 

 each stroke. 



The knife should be hard enough to support an edge, but not so 

 hard as to be brittle. The proper temper is about that given a 

 good razor. 



We need at least two hones one comparatively coarse, for 

 removing slight nicks, and another for finishing. The first part of 

 the work is best done by means of a sort of artificial hone made 

 of ground corundum. These are kept in stock by dealers in 

 mechanics' supplies, of great variety 'in size and fineness. For 

 razors a "00" corundum slip will best answer. This will very 



