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 



Fig. 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. 



