188 



INSTRUMENTS FOR MICROSCOPIC DISSECTION. 



Fig. 93. 



otherwise have too much ' spring ; ' much may be done by their 

 mere tearing action ; but if it be desired to use them as cutting 

 instruments, all that is necessary is to give them an edge upon a 

 hone. It will sometimes be desirable to give a finer point to such 

 needles than they originally possess ; this also may be done upon a 

 hone. A needle with its point bent to a right angle, or nearly so, 

 is often useful ; and this may be shaped by simply heating the 

 point in a lamp or candle, giving to it the required turn with a 

 pair of pliers, and then hardening the point again by re-heating it 

 and plunging it into cold water or tallow. 



136. Catting Sections of Soft Substances. — Most important 

 information respecting the structure of many substances, both 

 Animal and Vegetable, may be obtained by cutting sections of 

 them, thin enough to be viewed as transparent 

 objects. Where the substances are soft, no other 

 instrument is necessary for this purpose than a 

 sharp knife, which may be best made with a 

 thin two-edged blade like that of a lancet ; 

 considerable practice is needed, however, to make 

 effectual use of it ; and some individuals acquire 

 a degree of dexterity which others never succeed 

 in attaining. In cutting sections of Animal tis- 

 sues, which, owing to the quantity of water they 

 contain, do not present a sufficiently firm resist- 

 ance, it is often desirable to half-dry these, by 

 exposing small pieces freely to the air, with the 

 aid of a gentle warmth if required ; when this 

 desiccating process has been carried sufficiently 

 far, thinner sections can be cut than could pos- 

 sibly have been made in the original state of the 

 tissue ; and the texture, after a short macera- 

 tion in water, almost entirely recovers its 

 pristine characters. There are certain tissues, 

 however, which will not bear to be thus treated, 

 and of which it is sufficient to examine an 

 extremely minute portion ; and for making sec- 

 tions of these, such a pair of Scissors as is represented in 

 Fig. 93 will often be found very useful ; since, owing to the 

 curvature of the blades,* the two extremities of a section 

 taken from a flat surface will generally be found to thin away, 

 although the middle of it may be too thick to exhibit any structure. 



* It is difficult to convey by a drawing the idea of the real curvature 

 of this instrument, the blades of which, when it is held in front view, 

 curve — not to either side — but towards the observer; these scissors 

 being, as the French instrument-makers say, courbes sur le plat. — As an 

 example of the utility of such an instrument to the Microscopist, the 

 Author may cite the curious demonstration given a few years since, by 

 Dr. Aug. Waller, of the structure of the Gustative Papilla?, by snipping 

 them off from the living Human tongue, which may be done with no 

 more pain than the prick of a pin would occasion. 



Curved Scissors 

 for cutting Thin 

 Sections. 



