108 



THE ART OF MAKING MICROSCOPE SLIDES 



Microtomes 



Fig. 56. Sliding microtome. 



Fig. 57. Rotary microtome. 



controls the section tliickness must be so 

 moved that an exact number of microns is 

 indicated. If, for example, the knob is so 

 moved that the indicator Une hes between 

 9 and 10 microns, the pawl will not engage 

 the ratchet perfectly but ^\dll chip off a 

 small portion of brass at each revolution. 

 It only requires a few weeks' operation 

 under these careless conditions to destroy 

 the ratchet wheel which will have to be 



replaced at the factory. No inexperienced 

 student should ever be trusted with one 

 of these machines until the mechanism of 

 it has l)een explained to him and clearly 

 demonstrated. 



Knives and Knife Sharpening 



The most important single factor in the 

 production of good sections is the knife 

 used in cutting. It does not matter how 



