36 HISTOLOGY OF MEDICINAL PLANTS 
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 for- 
ward or backward in such a manner that the knife can be 
arranged with an oblique or right-angled cutting surface. 
The minor rotary microtome (Fig. 37) has a fixed knife, held 
in position by two pillars, and a movable object-carrier. The 
Fic. 37.—Minor Rotary Microtome 
object is firmly secured by a clamp, and it is raised by a microm- 
eter 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. 
CARE OF MICROTOMES 
When not in use, microtomes should be protected from dust, 
and all parts liable to friction should be oiled. 
