190 THE MICROSCOPE AND ITS REVELATIONS. 



elevate the substance to be cut, so as to make it project in an almost insen- 

 sible degree above the table, and this projecting part is to be sliced off 

 with a knife previously dipped in water. For many purposes an ordinary 

 razor will answer sufficiently well; but thinner and more uniform sections 

 can be cut by a special knife having its edge parallel to its back, its sides 

 slightly concave, and its back with a uniform thickness of rather less than 

 l-4th inch. Such a knife should be 4 or 5 inches long, and 7-8ths inch 

 broad; and should be set in a box-wood handle about 4 inches long (Dr. 

 S. Marsh). The motion given to its edge should be a combination of 

 draining 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 gradu- 

 ated, 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 care- 

 fully taken-off the knife, or floated-away from it, on each occasion, to 

 prevent it from being lost among the lamella of cork which are removed 

 at the same time. Vertical sections of many Leaves may be successfully 

 made in this way; and if their texture be so soft as to be injured by the 

 pressure of a cork, they may be placed between two half-cylinders of car- 

 rot or elder-pith. 



185. Hailes's Microtome. The foregoing simple form of Microtome 

 has received, at various hands, numerous modifications of detail, without 

 any essential change in its plan of construction. Its chief defect is, that 

 as the body to be cut is directly acted-on by the screw at the bottom of 

 the cylinder, its motion (if it be tightly held by the binding screws) is apt 

 to be jerky and irregular. To remedy this defect, Mr. H. P. Hailes has 

 devised an improved model, the essential feature of which is that the body 

 to be cut is secured within an inner tube, which, sliding freely within the 

 outer cylinder, is raised smoothly and equally by the micrometer screw 

 attached to the base of the latter, as shown in Fig. 134 (1, 2). The cut- 

 ting-bed formed by the flange B, is provided with two slips b of hardened 

 steel, on which, in ordinary section-cutting, the knife or razor slides 

 horizontally, as in the ordinary Microtome. But by the addition shown 

 in 3, 4, this instrument can also be effectively adapted for cutting thin 

 sections of substances hard enough to require the use of the saw. At the 

 back of the cutting-bed, there can be secured (by means of the screw and 

 and steadying-pins) a metal block, b l , which carries two guides # 2 , # 2 , of 

 hard steel; and these, when thus attached, lie over the two similar strips 

 fixed on the cutting-bed. By passing the blade of a fine saw between the 

 movable guides and the fixed strips, and screwing down the former 

 (which are raised by a spring) as far as will confine the saw without im- 

 peding its working, sections of Bone, Teeth, etc., may be cut as thin as 

 the nature of the substance will allow, and with a uniformity that with- 



