APPENDIX. 293 



being damped to the table. Its smaller size renders it 

 more handy to work with, and if it is necessary to inter- 

 mit the slicing for any length of time, the embedded tis- 

 sue can be preserved without injury by inverting the in- 

 strument into a beaker of spirit. 



Dr. Rutherford's freezing microtome (F"ig. 39) is 

 designed to enable sections to be made of a tissue 

 hardened by freezing. The instrument can also be used 

 as an ordinary microtome. It may be described as an 



Fig. 39. 



o 

 Rutherford's freezing microtome. 



B, Plate of gun- metal, with aperture, A. leading into well of micro tone; 0, lower 

 t'nd of cylinder in which the screw, D, works, moving a brass plug up or down ; 

 E, indicator for showing the fraction of a revolution imparted to the screw; 0, 

 trough to hold the freezing mixture, with H, tube to c induct away the water 

 produced by the melting of ihe ice ; F, clamp to fix the instrument to a table. 



improved form of Stirling's microtome with the addition 

 of a capacious metal trough which surrounds the upper 

 part of the cylinder. The trough is filled with a freezing 

 mixture (snow or pounded ice and salt, equal parts). 

 Into the well or tube of the microtome is poured a thick 

 solution of gum, which soon begins to freeze at the peri- 

 phery. The tissue to be cut (which may be either fresh, 

 or hardened by one of the ordinary methods, and should 

 preferably be soaked in gum for some hours previously), 

 is placed in the gum and held there until fixed by the 

 advancing congelation, and when the whole is uniformly 



