454 



Ott: A new Kotary Microtome. 



XXVIIL 4. 



The feed pawl is automatically lifted free from the teeth of 

 tbe wheel on the return stroke and this device is so arranged that 

 it holds the pawl away from the teeth all the time when the nut 

 on the feed screw has reached its limit. In this way any danger 

 of „jamming" the threads is avoided. The nut can be brought to 

 the other limit of the screw bringing the object holder back for a 

 new series of sections by turning a little crank {E) at the end of the 

 thread. This crank also serves the purpose of adjusting the object 

 to and from the knife with the nicety of a microscope fine adjustment. 



4. 



These accurate, unique and very practical features in the feed 

 mechanism itself would not avail so much if they were not accom- 

 panied by extreme rigidity in the other parts as well : — the object 

 clamp and the knife clamp in particular. 



The object clamp is a modified ball which fits into its socket 

 and is very rigidly held there by the ends of three set screws (AAÄ) 

 impinging on the flange projecting from the back surface of the 

 clamp as shown by the dotted lines in figure 3. By means of these 

 screws the clamp may be oriented to any desired position with a 

 delicacy and accuracy obtainable in no other clamp. 



The knife is held at either end by a clamp (A'C) which clamps 

 it along 30 mm of its edge as well as at its back, as shown in 

 figures 3 and 4, when the set screw (ß) which is threaded into 



