348 MANIPULATION. 



more completely by a steady pin seen at the base of the front 

 blade. The author, however, has found that if the blades be of 

 the shape represented by fig. 231, B, they will cut much better 

 than those having the edges rounded. When this instrument 

 is required to be used, the thickness of the section about to be 

 made wlU depend upon the distance the blades are apart ; this 

 is regulated by sliding up or down the rivet, a, as the blades, 

 by their own elasticity, will always spring open and keep the 

 rivet in place ; a cut is then to be made by it, as with an 

 ordinary knife, and the part cut will be found between the 

 blades, from which it may be separated either by opening 

 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 Needles. — These instruments differ but slightly 

 in shape from scalpels ; they are of two kinds, the straight 

 pointed and the curved, one of the former is shown at fig. 207, 

 page 305, and one of the latter by fig. 232. Both of these 



rig. 232. 



forms can be made sharp on a hone, and with either of them, 

 and a delicate pair of forceps, very excellent dissections of 

 small subjects, such as insects, may be made ; when used in 

 pairs, they will be found very serviceable in separating or 

 tearing asunder delicate animal and vegetable tissues under 

 the microscope; for this purpose a pair of the curved form 

 wiU be found most convenient. As substitutes for the instru- 

 ments just described, various kinds of needle-holders have been 

 contrived, three of the best of these are shown in fig. 233 ; 

 in all, needles of various shapes and sizes can be held firmly — 

 in the first and third the needle is secured by a sliding ring, 

 and in the second by two screws ; in the first and third also 

 the handle is hollow to contain needles, but in the second it is 

 solid. When needles are employed, they may be curved by 



