ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 233 
formation is facilitated, that section thickness can be varied within 
rather wide limits, and that resistance to the knife-action is reduced. 
Steam or hot water may be employed as the heat agent ; and attachment 
can be made to a reservoir of constant pressure or temperature. Great 
attention has been bestowed on the means of the automatic propulsion 
of the preparation. The upper arm of a jointed lever b, b , b, b bears 
on its left end a catch which engages with the small toothed wheel c 
(fig. 63). The wheel is connected with the micrometer-screw, and 
serves the relatively rougher advance of the preparations. A stroke 
of the coarse adjustment corresponds to an advance of the preparation 
Fig. Gt. 
of about 1/150 mm., as the micrometer-screw has a pitch of 1/2 mm., 
and the wheel 75 teeth. The movements of the lever are occasioned 
by the impact against the pins of a star block connected with a vertical 
pillar e (fig. 64). According to the position of the star, the wheel is 
advanced 1, 2, 3, 4, 5, 6, 9, 12, or 15 teeth, which correspond to the 
advance of the preparation of 6, 13, 20, 26, 33, 40, 60, 80, and 100 /x. 
The reading-off of the adjustment is by a millimetre scale whose indi- 
cator is visible to the right below / in fig. 64. The upper triangular 
part of the pillar is rotary, and is movable in the lower circular part, 
so as to put the parts out of action (as in fig. 64). The object can be 
fixed on any desired position of the slide by means of the screw g. 
1899 E 
