ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 



1083 



reduce the friction ; two fine rollers under the agate plate assure tho 

 perfect contact of the carrier with the sliding plane. 



The object-carrier is attached to an elevator which is raised and 

 lowered by the same mechanism as the slow motion of Continental 

 Microscopes. This is inclined so as to reduce the elevation and allow 

 of sections being made as fine as the knife will cut or the nature of 

 the tissues will permit. Special mechanism prevents loss of time in 

 the screw, and the thickness of the section is exactly indicated by 

 graduations on the milled head. At each traverse of the knife the 

 object is raised automatically as the knife-carrier strikes against the 

 end of a lever-arm which catches in the teeth of the wheel shown in 

 the figure, and which by means of a tangent screw at the other end of 

 its axis turns the micrometer screw and raises the object ■ 002 mm. 

 If it is desired to raise the object to a greater extent the knife-carrier 

 must be made to strike the eud of the lever a second or third time, 

 according to the height required. 



The microtome can also be used to cut sections in alcohol by a 

 very simple and entirely novel addition. A metal tray having an 

 aperture in the centre, over which a piece of indiarubber is stretched, 

 is placed on supports, as shown in fig. 239. The indiarubber is pierced 



Fig. 239. 



with a small aperture in which the vertical rod is applied which 

 supports the object-carrier, tbe edge of the rubber is then clamped by 

 a special arrangement which forms a kind of annular drumhead of it 

 and prevents leakage of the fluid. The object does not project above 

 the bottom of the tray which is filled with alcohol. 



In order that the knife may work easily in the tray, the blade is 

 set on an angle-piece so that it is 3 cm. below the handle. The 

 movements are thus left quite free ; the tray is in contact with the 



