ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
489 
to be cut. The object of the well is to give greater depth for the tissue 
than is possible with the shallow trough, and, at the same time, to 
economise spirit. The sides of the trough have two perfectly parallel 
wedge-shaped grooves for carrying the wedge-slides. The object of the 
double groove was to enable the knife, in cutting large sections, to be 
supported at both ends and from both sides of the trough ; but since the 
instrument has been in use it has been found that the knife can be 
perfectly well supported from one wedge-slide alone. The ends of the 
trough are closed with a thin layer of oak. 
The trough is made of cast iron in a single casting, and the grooves 
in the sides are planed by a planing machine. The wedge-slide W b is 
10 inches long, and is made of cast-iron. The sliding surfaces have been 
grooved so as to diminish friction in working. To the upper surface 
two long lever-arms H H, made of gun-metal, can be fixed. Those aie 
slotted throughout almost their entire length, so as to allow the knife to 
be placed at any desired degree of obliquity to the piece of tissue to be 
Fig. 78. 
cut. This adjustment can be effected with the greatest readiness, and 
the plane of the knife is thereby scarcely, if at all, altered. 
The knife K is hollow ground. Its blade is 12 in. long and 
If in. broad. Its ends have been cut obliquely so as to allow the 
point of the blade to come nearer the margin of the trough than would 
have been possible had the ends been rectangular. This is especially 
desirable when very large sections are to be cut. The knife can be fixed 
by a simple adjustable apparatus to the slotted arms (fig. 78). 
The screw for raising the object has forty turns to the inch. To 
its upper extremity is attached a ball-and-socket arrangement, into the 
former of which is screwed the clamp for holding the tissue. A special 
arrangement is provided for screwing the socket on to the ball to any 
desired degree of tightness. It is not difficult to screw the socket up 
so that it should be just so loose that the clamp can be easily moved 
into any desired position, and yet so tight that it shall retain that posi- 
tion during the process of cutting. 
The screw is raised by means of a toothed wheel (E, fig. 77) at its 
lower end, and this wheel, again, is turned by means of an arrangement 
of levers thrown into action by the impact of the wedge-slide at the end 
