ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



841 



ingenious, as will be evident from the following considerations. If 

 we watch any one making fine sections of a complicated object with 

 the free hand we see that at first the hand is held with the back 

 inclined downwards, and in a position somewhat similar to that 



Fig. 195. 



assumed on going to shake hands. From this the hand is gradually 

 changed during the cutting into a position inclined almost completely 

 upwards, and at the same time, if the operator is not left-handed, the 

 end of the knife describes an arc of 90° in the direction of a watch 

 hand, the part of the knife which is furthest from the hand having 

 the greatest rotation, whilst that where the knife is fastened to the 

 handle remains almost stationary. This movement cannot, for 

 mechanical reasons, be imitated in this microtome unless the guide of 

 the knife and of the preparation (on the inclined plane) is changed 

 from a straight line into one curved to the right, and at the same 

 time a combined circular movement is given to the block which serves 

 for fixing the knife, in which case a sickle-shaped knife fixed to the 

 shaft at an obtuse angle must be used. 



' The second or Banvier principle appears to be more practical 

 and capable of satisfying every requirement. Its origin is due to 

 Eanvier, but it has since been considerably improved by Welker, 

 Beetz, Gasser, Gudden, Schiefierdecker, and others. It is to this 

 form that the author's modifications have been applied. 



" As modified, it has the form represented in Fig. 196, and consists 

 of two separable parts — (1) the microtome-cylinder proper, with its 

 micrometer-screw for raising the preparation, and (2) a clamp which 

 fastens the cylinder to the table (Fig. 197). The latter has a divided 

 ring (seen in the upper left corner of the figure), which by a screw can 

 be firmly attached to the neck of the cylinder. It is essential that 

 the cylinder and the clamp should be capable of being detached, both 

 for enabling the instrument to be cleaned, and also for altering the 

 position with respect to the table of the object imbedded in the 

 cylinder. 



" The modification consists, therefore, in this : Instead of the 

 microtome being held in the hand (Eanvier), or fixed in a water reser- 



