286 Transactions of the Society. 



motion than has the feed nut. At its lower end tlie connecting 

 pin seats into a conical hole in the feed lever and at its 

 upper end into a conical hole in the swinging arm. This pin is 

 kept in compression and in geometric contact with both the feed 

 lever and the swinging arm by means of a spring. It will be 

 seen that this pin remains approximately vertical throughout the 

 motion, and that che swinging arm is kept at a constant height 

 during the cutting stroke, owing to its point of contact with the 

 feed pin being on its axis. 



Flat Sections. 



In the Eocking Microtome the sections are cut from a cylin- 

 drical surface of 90 mm. radius. If the section is 5 mm. in 

 diameter the maximum deviation of the surface of the cylinder 

 from a plane is ' 035 mm. This is a small amount, and probably 

 with soft tissues the deformation of the parts from the normal 

 position caused by embedding or freezing is far greater than this. 

 The advantage gained by cutting flat sections is sometimes more 

 imaginary than real, but it is not infrequently some advantage, 

 and with large sections it is well worth havincr. 



Horizontal Sections. 



The plane of the sections is horizontal ; this is advantageous 

 for paraffin embedded sections as the correct orientation of the 

 object is far easier, and this position is essential for celloidin 

 embedded sections as the lubricating liquid remains on the knife, 

 and it is possible to float off the sections, which is not the case 

 where the side of the knife is in a vertical plane. For frozen 

 sections a horizontal position is essential. A dissecting lens and 

 stand can be conveniently used during the precise orientation of 

 the object. Eibbons of paraffin embedded sections can be made 

 witli ease by this microtome, although perhaps their manipulation 

 requires slightly more care than with the Eocking Microtome. 

 The clamps for the knife have been designed to project only a 

 little above the knife itself, and so do not interfere with the con- 

 venient use of tlie section lifter ; thus delicate handling of the 

 sections is simpler, and the danger of damaging them is lessened. 



Uniform Sections. 



In all cases successive sections should be as nearly as possible 

 of equal thickness, and each section should be of the same thick- 

 ness throughout. With a good well-sharpened knife a section in 

 paraffin can be cut as thin as 1 micron. If the sections with a 



