156 K. P. WILLIAMS ON CUTTING FRESH FROZEN TISSUES. 



you will see that the new surface is of prime importance, and 

 until it is brought parallel with the facing plate there must be a 

 positive displacement, without any cutting if the setting screw is 

 not advanced enough. I do not think that there is much more to 

 be said about the razor frame, except that by the movement of the 

 base screws and those at the razor edge, the blade can be brought 

 into parallelism with the facing plate over which it moves. Revert- 

 ing to the other part of the apparatus. It consists of a wooden 

 chamber with a thick bottom, to which is firmly screwed a pillar 

 with a spreading base, and curved sides so as to increase the 

 extent of surface in contact with the freezing mixture (ice and 

 salt). This cylinder projects above the facing plate, and the top 

 has a hole drilled and tapped in it to receive discs of any size ; this 

 arrangement allows the use of wax or cement for any substance 

 which may not require to be frozen, in which case you would 

 select a disc of convenient size ; hold it over the spirit lamp, and 

 cement your object upon it, adjusting it as occasion may require, 

 screw it into its place, and cut away. To the top of the chamber 

 is fitted a turned lid, with a projecting flange ; the lid is turned 

 out on the top to receive an 8 inch plate-glass disc, with a hole in 

 the centre, 1^ inch in diameter. A bead is left up around the 

 external edge, and a ring of ebonite is turned into the centre hole, 

 also projecting above the surface of the plate-glass ; the object of 

 this being to prevent the slipping of the razor frame off the plate 

 to the probable damage of the razor edge. I do not think I need 

 further commend this matter to your notice. I may, however, in 

 conclusion, say that I should feel happy indeed if anything I have 

 done should prove of any service whatever to microscopy, especially 

 in relation to that most useful, and, if I may be allowed to say, 

 most legitimate application of the instrument — the study of the 

 organic tissues. 



DESCRIPTION OF PLATE XIV. 



Fig. 1. — Section of chamber, cylinder, &c. The chamber is filled with ice 



and salt. 

 Fig. 2. — The triangular frame, S the setting screw, B B base screws, C C 



razor edge screws, notched at the point, the notches corresponding . 



to others in the razor edge. 

 Fig. 3. — Diagram of razor edge. 



