160 PRACTICAL HISTOLOGY. 



292. Scissors are in almost constant requisition for 

 removing small portions of soft tissues for microscopical 

 preparation. The most convenient form is that shown in 

 Fig- 55- 



FIG. 55. Fine scissors for microscopical purposes. 



293. Valentin's Knife was formerly much employed 

 for making thin slices of organs, such as the kidney, lung, 

 stomach, etc., in the fresh condition. It consists (Fig. 56) 

 of two parallel blades. In using the knife, these are first 

 clamped in close apposition by the wedge a. They are 

 then opened to any desirable distance by the screw b, and 

 are, of course, fixed by the forces of the wedge and the 

 screw acting in opposite directions. The thickness of the 



FIG. 56. Valentin's knife. 



slice depends on the distance between the blades. The 

 sections obtained by this knife are far inferior to those made 

 with a freezing microtome, but nevertheless it is useful when 

 the microtome cannot be employed. 



294. Single-bladed knives. A razor and a scalpel 

 are the knives most commonly used for cutting any tissue 

 which by softening or hardening has been brought to a suit- 

 able consistence. The " army razors," made by Heifor of 

 Sheffield, are the most convenient for all ordinary purposes. 

 They are made of good steel a most essential point and 

 their blades are thin and broad enough to give good sections. 

 Similar razors, made for section-cutting by Weiss of London, 



