ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 



915 



enhanced its usefulness by causing the spring to catch at pleasure 

 either in each of the fifteen divisions of the drum or in a whole or half 

 or l-3rd turn of the screw. 



By an improvement in the object-Tiolder the object is now movable 

 in all three directions of space. It is raised in the vertical direction 

 and turned round the vertical axis by the hand ; in the two other 

 planes it is moved by rack and pinion, so that changes in direction 

 can be conveniently and accurately made during the cutting. As 

 fig. 171 shows, the piece of paraf&n is at the top of a hollow metal 



Fig. 171. 



cylinder, which is filled inside with paraffin. The cylinder can be 

 pushed up and down in the block a, and by means of six holes beneath 

 and a small metal rod can be turned in it. It is held fast in all 

 positions by a clamp 6. The turning of the block in the frame c round 

 the horizontal axis is effected by d, and it is fixed by the small screw 

 e (the head of which is provided with holes for the small metal 

 rod), which presses one bearing of the block against its axis. In 

 the same way the frame is turned round the long axis by the rack 

 and pinion on the left and fixed by the screw /. By the pressure of 

 the bearing on the axis, the position of the object is altered at the 

 most • 005 mm. 



The arrangement is in fact only a modification of the Cardani 

 ring, used with ship lamps, &c. With this microtome alone is it 

 possible to alter the direction of the object at pleasure, without at the 

 same time raising or lowering it much. The latter disadvantage is 



