294 J. w. GROVES ON Williams' microtome adapted 



freezing apparatus. A and B are respectively the razor frame, with 

 the razor in situ, and the bowl-cover with the glass plate top upon 

 which the razor frame is moved. It will thus be seen that the whole 

 of the section-cutting part of the machine is identical with that for- 

 merly used with ice and salt. The central brass cylinder, instead of 

 being solid, is hollow, so that the Ether spray may play up the 

 inside and impinge upon the lower surface of the brass plate I, upon 

 the upper surface of which the material to be frozen is placed, In 

 the figure, the hollowed cylinder is seen to open below into the Ether - 

 containing chamber, into the lower part of which opens a horizontal 

 tube, which turns up at right angles and ends in a funnel-shaped 

 extremity (G), over which screws a cap. 



In the centre of the bottom of this chamber is a circular aperture 

 closed by a piece of brass tubing, which passes up vertically to end 

 in a cone with a very small aperture, and having another small hole 

 in its side towards the bottom. The lower end of th's tube is 

 plugged, and through the plug (E) passes vertically a very fine 

 tube, which is continuous inferiorly with the tube from the apparatus 

 for pumping in air. This consists of an india-rubber pump (F), con- 

 nected by a short piece of tubing with a slightly distensible ball 

 covered with netting, and from the opposite side of which a piece of 

 india-rubber tubing passes on towards E. In the side of the large 

 hollow cylinder of the machine is inserted a small tube connected 

 with a length of pipe (H) for the escape of the spray after use. 



The method of freezing with this microtome is as follows : — After 

 the material has been partially hardened, and the hardening agent 

 removed, place it on the brass plate (I) with a little gum mucilage ;* 

 then unscrew the cap (G), fill the chamber with Ether, replace the 

 cap, and commence pumping by pressing the ball (F) vigorously 

 and rapidly in the palm of the hand. Air will thus be pumped 

 into the net-covered ball, from which it will issue in a continuous 

 jet along the india-rubber tube, up the small tube, through the plug 

 E, and again through the hole at the apex of tlie conical-ended 

 vertical tube, to pass straight up against the under surface of the 

 plate I. The rush of air thus produced causes pressure on the 

 surface of the Ether, and also tends to produce suction at the space 

 between the small central tube and the one which has the conical 

 extremity, so tliat the Ether passes through the hole in the side of 

 the latter tube, rises in the space between the two tubes, and is 



* If the material is quite fresh the mucihige may be dispensed with. 



