206 PREPARATION OF OBJECTS. 



This instrument essentially consists of an upright hollow cylinder 



of brass, with a kind of piston 

 FlG - 59 which is pushed from below 



upwards by a fine-threaded 

 screw, turned by a large milled 

 head; at the upper end, the 

 cylinder terminates in a brass 

 table, which is made to present 

 a perfectly flat surface. At one 

 side is seen a small milled head, 

 which acts upon a "binding- 

 screw," whose extremity pro- 

 jects into the cavity of the cylin- 

 der, and serves to compress and 

 steady anything that it holds. 

 A cylindrical stem of wood, a 

 section instrument. piece of horn, whalebone, carti- 



lage, &c., is to be fitted to the 



interior of the cylinder, so as to project a little above its top, and 

 is to be steadied by the " binding-screw ;" it is then to be cut to 

 a level by means of a sharp knife or razor, laid flat upon the 

 table. The milled head is next to be moved through such a por- 

 tion of a turn, as may very slightly elevate the substance to be 

 cut, so as to make it project in an almost insensible degree above 

 the table ; and this projecting part is to be sliced off with a knife, 

 previously dipped in water. The best knife for this purpose is a 

 razor, ground flat (instead of concave) on one side, but having 

 still a concave surface on the other ; the flat side is to be laid 

 downwards upon the table ; and the motion given to the edge 

 should be a combination of drawing and pressing. (It will be 

 generally found that better sections are made, by working the 

 knife from the operator, than towards him.) When one slice has 

 been thus taken off, it should be removed from the blade by 

 dipping it into water, or by the use of a camel-hair brush ; the 

 milled head should be again advanced, and another section taken ; 

 and so on. Different substances will be found both to bear and 

 to require different degrees of thickness ; and the amount that 

 suits each can only be found by trial. It is advantageous to have 

 the large milled head graduated, and furnished with a fixed 

 index ; so that this amount having been once determined, the 

 screw shall be so turned as to always produce the exact elevation 

 required. Where the substance of which it is desired to obtain 

 sections by this instrument, is of too small a size or of too soft a 

 texture to be held firmly in the manner just described, it may be 

 placed between the two vertical halves of a cork of suitable size 

 to be pressed into the cylinder; and the cork, with the object it 

 grasps, is then to be sliced in the manner already described, the 

 small section of the latter being carefully taken oft the knife, or 

 floated away from it, on each occasion, to prevent it from being 



