ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 



683 



Fio. 104. 



of sections for large classes, and also for the rapid preparation of series of 

 sections in ribbons in embryological work, in which the element of time 

 becomes a serious consideration. One hundred sections per minute can be 

 readily cut with it. 



The device is small and compact and is also automatic; the cutting 

 takes place as fast as it is possible to move a vibrating lever up and down 

 through a distance of 3 in. with the right hand. The designer considers 

 that "nearly all other automatic microtomes are costly, unwieldy, large, 

 and heavy, or else very compli- 

 cated and liable to get out of 

 order. The only exception in 

 part to this rule is the rocking 

 microtome, made in Cambridge, 

 England ; but it cuts in an arc, so 

 that the sections are segments of 

 a hollow cylinder, and not parts 

 of a perfect plane ; besides, the 

 rocking or vibrating arm admits 

 of only a very limited movement, 

 so that the instrument is suitable 

 only for cutting sections of ob- 

 jects of very limited dimensions ; 

 nor is the position of the block 

 adjustable. Moreover, in none of the automatic microtomes now in use is 

 it possible to place the knife at right angles or any other desired angle to 

 the direction in which the block to be cut is moved — a great desideratum 

 in botanical or other work in which an inclined knife is necessary. In 

 order to supply an instru- 

 ment serviceable especially Fig. 195. 

 to teachers, as well as to all 

 classes of students, bota- 

 nists, pathologists, histolo- 

 gists, and zoologists, the 

 designer has attempted to 

 bring together all the de- 

 sirable features of previously 

 invented instruments, in as 

 simple, convenient, and com- 

 pact a form as possible, 

 without sacrificing rapidity and efficiency of action." 



The working parts are an oscillating lover, which is provided with a 

 clamp at one end into which paraffin-holders are adjusted, and at the other 

 with a simple handle. This lever rests upon trunnions on either side, and 

 these in turn rest in triangular notches at the top of the two pillars between 

 which the lever oscillates. At the cutting end of the lever a spring pulls 

 the lever down and effects the sectioning and also the adjustment for the 

 next section. The lever is pushed over and adjusted for the successive 

 sections by a hollow screw, through which passes the trunnion on the side 

 away from the knife. This screw is fixed to a toothed wheel, 3 in. in 

 diameter, which revolves close by the side of the oscillating lever. The 

 toothed wheel and screw is actuated by a pawl fixed to the side of the lever 

 near the handle. The number of teeth which this pawl can pass in a single 

 vibration downward is controlled by a fixed stop screwed into the under 

 side of the oscillating lever near the handle ; the end of this stop striking 

 on the top of the bed-plate thus brings the lever to rest at a constant point 



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