284 Transactions of the Society. 



action and appearance from most other microtomes, and we will 

 first give a short description of it, and then the reasons wliy we 

 consider the special construction is advantageous, and further 

 details of some of its parts. 



Brief Description. 



The microtome (see fig. 1), which is made almost wholly of cast 

 iron, has a circular base 250 mm. in diameter, with three cork feet 

 which rest on the table. The object moves and the knife is fixed. 

 The knife is machine ground and is clamped at botli ends to the 

 knife-holder, but can be slid longitudinally in the holder to bring 

 a different part of its edge into action, it' one part is blunted. Its 

 cutting edge is horizontal, and can be adjusted to give the best 

 angle of cut. The knife-holder can be moved laterally and clamped 

 to the base at any convenient position. It can be also rotated 

 about a vertical axis so as to give a slicing cut — that is, the direc- 

 tion of the cutting edge of the knife can be placed at an acute 

 angle to the direction of the movement of the object. The object 

 is fixed in an orientating object-holder, very rigid in construction 

 and carried at the outer end of a iiorizoiital swinging arm. This 

 swinging arm can rotate at its inner end about a vertical axis. 

 Thus the object moves in a horizontal plane along the arc of a 

 circle and not in a straight line. The action is like the swinging 

 of a gate with the object carried at a point near the latch. In the 

 microtome the hinges are constructed so as to allow both rotation 

 and movement along the vertical axis of rotation of the hinges. 

 It is by means of this vertical sliding movement that the object is 

 raised between successive s^tions. The micrometer screw and nut 

 for giving this vertical movement to the object are similar to that 

 used in the Eocking Microtome. The method of feeding the screw 

 forward and the handle for moving ihe object past the knife are 

 also similar. In the new microtome the feed screw A (see fig. 2) 

 is ap})roximately vertical and is given a small rotary motion at the 

 end of each stroke from a pawl B, orried on the oscillating handle 

 C, which pawl engages with a large steel ratchet wheel D at the 

 lower end of the screw. This partial rotation elevates the feed nut 

 E on which is carried the outer end of the feed lever F. The 

 design is such that this nut cannot rotale about the feed screw, but 

 is free to rock with respect to the feed lever as it rises. Tlie feed 

 screw is supported in a conical seating at its lower end so that the 

 nut and screw can adapt themselves to tlie movements of the feed 

 lever. Tlie large end of this lever which extends across the micro- 

 tome is supported on horizontal knife edges, working on planes of 

 the same design as the vertical knife edges and planes of the 

 swinmn<4 arm. The axes of these two sets of knife edc^es are 



