96 



THE MICROSCOPE. 



the blades, from which it may be separated either by open- 

 ing them as wide as possible by the rivet, or by turning 

 them apart in the manner before described, and floating 

 the section out in water. 



Dissecting Scissors. In addition to the forceps and 

 knives, scissors will be necessary for the purposes of dissec- 

 tion : of these the most useful are shown in fig. 65. They 



Fig. 65. Dissecting Scissors. 



are made both straight and curved ; of the first kind, two 

 pairs will be required, one having the extremities broad, 

 and the other sharp-pointed ; if large dissections be under- 

 taken, a still stronger pair, with the extremities broad, 

 and made rough like a file, will be necessary. In dis- 

 secting under the microscope, the curved-pointed pair 

 shown at / are the most convenient. In all of these 

 instruments the points should fit accurately together : 

 sometimes those that are very sharp are apt to cross ; this 

 may in a great measure be prevented by having the branches 

 wide at the base where they are riveted. The points can 

 be sharpened on a hone, and a magnifier employed to 

 examine if they fit closely together. 



Fig. 66 represents Mr. Gibbon's " Section-cutting Ma- 

 chine." It consists of a stout brass frame, A A, having 

 an opening in the top plate, for a tube B, half an inch in 

 diameter, and in depth one and a half inches. In this 

 tube a loose piston, c, works freely, and is steadied by the 

 slot seen in it. To a female screw z>, motion is given by 

 the toothed wheel ; and the teeth of which, E, answer 

 the triple purposes of thumb-milling, ratchet- stop, and 



