THE ROCKING MICROTOME 469 



knife, it is then fixed in this position by the screw o (scarcely evident 

 in the illustration). 



This done, the spirit-vessel S/> can be arranged in a position 

 which will not interfere with the free movement of the knife. In 

 order that a stream of spirit may follow the knife over the object, 

 the following arrangement, is adopted. The spirit-vessel Sp turns 

 round an axis on the column h ; to it is joined the arm L, which 

 carries in front the fine tube r (connected with t #), and also the rod 

 p ; the latter is movable perpendicularly, and to its lower end a 

 bridge or grip with two small rollers i and i' is fastened. The rod 

 ;; is so placed that on each side of the metal strip b, screwed on to 

 the knife-support, there is one o the rollers. By the adjusting 

 screws Stf, the whole apparatus is so*arranged that, when the knife- 

 carrier is in motion, no other friction occurs than that of the rollers 

 on the strip b b b. 



The vessel is filled by screwing off the head Z. As the tube r 

 acts as a siphon, it is necessary, when the cock is turned on, to blow 

 down the tube. The stream of spirit should be directed at a right 

 angle to the knife, and about the middle of the object. This done, 

 the object 06, by means of the screw K, is firmly grasped in the fangs 

 of the object-carrier ; the correct direction for the position of the 

 knife is given to its surface by the screws at f and f\, and then 

 the axes of the fangs are tightened up by the levers q and q 1 '. If 

 the height of the object is not quite correct, adjustment is made by 

 the screw r m. By turning the screws S, S the holder is fixed. 



Y is a wheel with cranked axle E?c, and this by means of a cat- 

 gut band moves the knife. 



For the ri>'xl production of ribbons of sections, however, the 

 instrument par excellence is the Cambridge rocking microtome. It 

 is illustrated in fig. 399. 



The principle is the employment of a rotary instead of a sliding 

 movement of the parts. Two uprights are cast on the base-plate, 

 and are provided with slots at the top, into which the razor is placed 

 and clamped by two screws with milled heads. The inner face of 

 the slot is so made as to give the razor that inclination which has in 

 practice been found most advantageous. The razor is thus clamped 

 between a flat surface and a screw acting in the middle of the blade, 

 and the edge of the razor is consequently in no way injured. 



The imbedded object is cemented with paraffin into a brass tube 

 which fits tightly on to the end of a cast-iron lever. This tube can 

 lie made to slide backwards or forwards, so as to bring the imbedded 

 object near to the razor ready for adjusting. It is now furnished 

 with a mechanical arrangement for accurately adjusting the position 

 of the object. The cast-iron lever is pivoted at about 3 in. from the 

 end of the tube. To the other end of this lever is attached a cord 

 by which the motion is given, and the object to be cut brought 

 across the edge of the razor. The bearings of the pivot are 

 V-shaped grooves, which themselves form part of another pivoted 

 system. 



Immediately under the first pair of V's is another pair of inverted 

 Vs. which rest on a rod fixed to two uprights cast on the base-plate. 



