452 



Ott: A new Rotary Microtome. 



XXVIII, 4. 



very solid bearing by means of the feed screw (FS). As the 

 point (P) moves toward tlie balance wheel ( W) the object is forced 

 forward one half as far, and it is independent of any movement in 

 the direction of the arrows of the block (B) and also provides an 

 inclined plane feed which has heretofore proven so successful. The 

 total excursion of the feed is 37 mm, — double that of most micro- 

 tomes. The feed mechanism may be set to cut any thickness from 

 one to sixty microns. The desired thickness is obtained by turning 



1. 



the button (Ä') until the number representing the thickness sought 

 appears opposite the index in the opening of the case (/, lig. 3). 



To obviate any liability of momentum vitiating the accuracy of 

 the sections , the feed screw is provided with two ratchet wheels, 

 the teeth of which run in opposite directions. The feeding pawl (FP) 

 works into the teeth of one wheel. A checking pawl engages the 

 other wheel for an instant at the end of every feeding stroke thereby 

 bringing the feed screw to a definite stop for every sectiou. This 

 feed mechanism is so arranged that the feeding always takes place 

 when the object is above the knife so that there is no danger of 

 forcing the face of the paraffin block against the knife on the np- 

 w;trd stroke. 



