ZOOLOGY AND BOTANY, MIOB0800PY, ETC. 



697 



usual way, an assistant working the lever alternately with the cut- 

 ting. The thickness of the cutting is controlled by the regulator, as 

 shown on the index ; the thickness most generally employed is twit ^^ 

 an inch. (These measurements are approximal.) The temperature at 

 which the best results have been attained has been where the surround- 

 ing atmosphere was about 40° Fahr. If during cutting the tissue 

 becomes softened, it must be refrozen ; this is accomplished by dis- 

 engaging both pawls, and causing the plunger to descend rapidly 

 by turning the micrometer screw direct by the knob on the ratchet- 

 wheel. The cylinders being interchangeable, the tin cylinders are 

 slipped over the brass ones previous to interchanging them ; thus 

 no delay takes place. Two hundred sections have been successfully 

 cut in a single minute, but a more moderate rate of about 100 per 

 minute is recommended. 



Figs. 162 and 163, one-fourth original size, show the instriunent 

 arranged for freezing with ether spray, rhigoline, &c. In Fig. 162, 



Fig. 162. 



( ^Y-,Y,-,>'^' 



Fig. 163. 



A is the zinc cylinder or spray chamber ; B, false or sloping bottom 

 for conducting condensed ether; D, exit tube leading to collecting 

 bottle ; C, object to be frozen ; E, ether spray apparatus ; F, pyra- 

 midal bed-plate, &c. In Fig. 163, A is the zinc cylinder ; B, plunger 

 of microtome ; C, opening for spray instrument, &c. ; D, exit tube 

 for collecting condensed ether; E, roughened top, to facilitate the 

 retention of the frozen object in position. 



Williams's Freezing Microtome.— This (Fig. 164), the design 

 of Mr. J. Williams, and made by Messrs. Swift, consists of a wooden 

 " tub " pitched inside (holding about 2 pints) to receive the freezing 

 mixture, having in the centre a brass standard, into which screw 

 the brass circular plates on which the material to be frozen is 



