916 SUMMARY OF CUERENT RESEARCHES RELATING TO 



present in Spengel's otherwise very good microtome * so tbat on 

 altering tbe direction of the section a considerable amoimt of shifting 

 is necessary. Both axes are therefore passed through the middle of 

 the upper surface of the block, as near as possible to the object. The 

 attachment of the object on a cylinder which is movable in a vertical 

 direction has the great advantage that pieces of more than 2 cm. in 

 length can be cut. At the beginning the cylinder is placed as 

 low as possible, and raised later on as required. Plates from 0*5 

 to 1 cm. deep can also be used under the knife and afterwards 

 removed. 



The latest modification relates to the points on which the slides 

 run. These have now been made of ivory, and the sliding surfaces 

 of the so-called bronze. In consequence of this the instrument is no 

 longer subject to rust, and the movement of the knife-carrier, which 

 when very slow, becomes irregular, is now, by the increased friction, 

 quite regular. The durability of this new combination is of course 

 undetermined, it seems, however, as if the wearing away of the 

 bearing surfaces were less than formerly, when metal was used upon 

 metal. 



Andres, Gieshrecht, and Mayer's Section-stretcher.t — A. Andres, 

 W. Giesbrecht, and P. Mayer describe a section-stretcher which they 

 consider to be superior to that of F. E. Schultze.J The latter, consist- 

 ing of a small cylinder and a watch-sj^ring, is fixed to the object-slide 

 of the microtome, and as the parafiin diminishes in height, the 

 cylinder exercises a decreased pressure and will not therefore work 

 uniformly during the whole process. Whilst the authors gave up a 

 similar apparatus on account of the above drawback, Schultze on the 

 other hand rejected an instrument similar to theirs in favour of his 

 own. 



The apparatus of the authors is attached to the knife itself, and 

 during the cutting maintains the same position with respect to the 

 section which it had in the beginning. It consists (fig. 172) of a 

 cylindrical steel rod / which is exactly parallel to the knife-edge, and 

 is just over it, and so that if further depressed the lowest line of its 

 surface would fall exactly on the knife-edge (j. It thus comiiels the 

 section to pass between it and the edge. The position of the rod 

 parallel to the edge of the knife in the vertical plane is adjusted by 

 turning its arm in the holes c or c' ; the jiarallel position in the hori- 

 zontal plane by the screws a and a\ which work against the back of 

 the knife ; and the vertical distance from the edge, which must be 

 regulated according to the thickness of the section, by the screw 6. 

 The whole apparatus is held on the knife by two clips jDressing on the 

 under surfaces. The hinge d d enables the rod and its support to be 

 turned back by means of the handle e so that the edge of the knife and 

 the rod / can be cleaned if necessary. For sections of great extent a 

 very thick rod is supplied, and for very small sections a thin rod 

 which can be easily attached. 



* Zool. Anzeig., ii. (1879) pp. 641-8. 



t MT. Zool. Stat. Neapel, iv. (1883) pp. 129-32 (1 fig.). 



X Cf. this Journal, ante, p. 450. 



