[Illustration: FIG. 36.--Base Sledge Microtome]
The =base sledge microtome= (Fig. 36) has a heavy iron base which supports a sliding-way on which the object-carrier moves. The object-carrier is mounted on a solid mass of metal, and is provided with a clamp for holding the object. The object is raised by turning a knob which, when turned once, raises the specimen one to twenty microns, according to how the feeding mechanism is set.
Sections thicker than twenty microns may be obtained by turning the knob two or more times. The knife is fixed and is supported by two pillars, the base of which may be moved forward or backward in such a manner that the knife can be arranged with an oblique or right-angled cutting surface.
[Illustration: FIG. 37.--Minot Rotary Microtome]
The =Minot rotary microtome= (Fig. 37) has a fixed knife, held in position by two pillars, and a movable object-carrier. The object is firmly secured by a clamp, and it is raised by a micrometer screw. The screw is attached to a wheel having five hundred teeth on its periphery. A pawl is adjusted to the teeth in such a way that, when moved by turning a wheel to which it is attached, specimens varying from one to twenty-five microns in thickness may be cut, according to the way the adjusting disk is set. When the mechanism has been regulated and the object adjusted for cutting, it is only necessary to turn a crank in cutting sections.
When not in use, microtomes should be protected from dust, and all parts liable to friction should be oiled.
Microtome knives should be honed as often as is necessary to insure a proper cutting edge. After cutting objects, the knives should be removed, cleaned, and oiled.
It should be kept clearly in mind that special knives are required for cutting collodion, paraffin, and frozen and woody sections. The cutting edges of the different knives vary considerably, as is shown in the preceding cuts.
Little attention is given in the present work to micro-chemical reactions for the reason that their value has been much overrated in the past. A few reagents will be found useful, however, and these few are given, as well as their special use. They are as follows:
=Distilled Water= is used in the alcohol, glycerine, and water mixture as a general mounting medium. It is used when warm as a test for inulin and it is used in preparing various reagents.