APPENDIX. 



293 



Microtomes. A section-cutting apparatus or microtome is essential for 

 liistological work. Several kinds are made, but those which I have found 

 most generally useful are the freezing microtome, the rocking micro- 

 tome of the Cambridge Scientific Instrument Company for objects which 

 have been embedded in paraffin, and the sliding microtome for celloidin- 

 embedded tissues. The action of the rocker is automatic ; that is to 

 say, every to-and-fro movement of the handle, H, not only cuts a section of 

 the tissue of definite thickness, but also moves the paraffin block forwards 

 in readiness for the next section. And by employing a rectangular block 

 of paraffin of the proper consistency, a long series of sections of the same 

 object, of equal thickness, can be obtained and made to adhere together in 



ROCKING MICROTOME. 



a riband (as shown in the figure). The sections can, if desired, be kept in 

 series by the employment of the creasote-shellac, or some other adhesive 

 method of mounting the riband. 



In the freezing microtome the tissue, after being soaked in gum-water, 

 is placed on a metal plate and frozen by playing an ether spray on the under 

 surface of the plate. The plate is moved upwards by a finely cut screw, 

 and the knife or plane used to cut the sections is guided over the plate by 

 passing over glass slides. In using the freezing microtome, especially for 

 the nervous system, it is important not to freeze the tissue too hard, or the 

 section will roll up like an ice-wafer. 



For celloidin-embedded preparations it is necessary to cut the sections 

 with a knife kept wetted with spirit. For this purpose a sliding microtome, 

 in which the knife or razor is moved horizontally over the tissue, with the 

 edge obliquely inclined to the direction of movement, is most useful. That 

 designed by Thoma, and made by Jung of Heidleberg, is admirably con- 



