MOUNTING AND PREPARATION OF OBJECTS. 67 



the ends of the fingers of the left hand are placed on 

 the opposite extremity of the razor from the handle, 

 the edge of the razor near the left hand fingers is 

 applied to the near side of the gum cylinder, and 

 passed through it from point to heel. The edge 

 during this manoeuvre being lightly applied to the 

 brass table, while the back is slightly elevated above 

 it. 



The thickness of the section depends on the dis- 

 tance through which the screw is turned, if the latter 

 be graduated, which is very easily done, the exact 

 thickness may be regulated. To graduate the screw 

 a measure is placed in the cylinder, and the number 

 of turns required to elevate the piston a quarter of 

 an inch, counted. If it takes twenty-five, every 

 revolution of the screw, elevates the cylinder one- 

 hundreth of an inch. A mark is now made on the 

 milled head of the screw, and the end of the cylinder 

 round which it works is divided (round its circumfer- 

 ence) into five equal parts. The mark on the screw 

 when it moves through one of these divisions raises 

 the section one five-hundreth of an inch, a thinness 

 rarely attained in section cutting. 



Several sections being cut by this method without 

 stopping to remove them singly from the razor, the 

 razor with the sections on it, are placed in the dish 

 containing the spirit and water; after a minute or 

 two and a little gentle agitation they will float off, 

 any that adhere being cautiously displaced with the 

 camel's hair brush. 



When a sufficient number of sections are cut, they 



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