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SUMMARY OF CURRENT RESEARCHES RELATING TO 



respectively. For most purposes the small size suffices. When hand- 

 motion is desired, a hent pin is fastened to the block (fig. 154) by 

 means of the same screw which holds the knife-clamp. For chain-use 

 the microtome is provided at each end with a beam-like projection, each 

 of which carries a chain-wheel, one for the winch, the other for the 

 straining of the chain. The winch can be fitted as shown in fig. 155, 

 •or at the other end, and thus an operator can rotate the winch either 

 with his left hand or his right. Fig. 154 shows the manner of the 

 automatic elevation of the object. The rotation of the tooth-wheel 

 occurs indirectly through a bent curved movable lever screwed to the 

 block (hence the "block-angle"). The lower end of the lever in the 

 movement of the slide to the end of the track engages with a spring- 

 hook, which itself engages in the teeth of the wheel and moves it on 



Fig. 155. 



one notch. The length of the stroke, about which the block-angle 

 rotates the wheel in this way, is dependent on the downward lever-end. 

 The length is longer or shorter, as the block-angle is steeper or more 

 oblique. The block-angle is arranged by the help of a small clutch 

 which is set to the small scale at the lever-end, the numeration 

 corresponding to the number of the wheel-teeth rotated at that par- 

 ticular position of the block-angle. A wheel-tooth corresponds to a 

 section thickness of ■ 001 mm. In its steepest position the block-angle 

 corresponds to a wheel-rotation of 25 teeth, and the section thickness is 

 then 25 /x. The forward movement of the clutch results from the 

 action of the spiral spring visible in fig. 154, the clutch sliding over the 

 teeth until a resistance is met with on the vertical wall of the micro- 

 tome. In order that the tooth-wheel should not move too easily, a 

 small brake (not shown in figure) is applied and regulated by a screw. 

 For facilitating the adjustment of the object-holder the female-screw 



