ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
243 
The angle and both ends are perforated for capped interchangeable 
screws, each having ten turns to the inch, one of these being the micro- 
meter screw. The blade, fig. 40, 7 j, is fastened to the long arm by the 
screw l, so that its edge is parallel to the short arm fg. The sliding 
piece moves along the glass plate, carrying the knife over the specimen 
to be cut, and the knife is lowered by turning the micrometer screw. The 
Fig. 40. 
thickness of section is obtained as follows : as one turn of the micrometer 
screw lowers the long arm 1/10 in., and as the distance between knife 
and short arm is one-fifth the length of e /, the knife is lowered 
1/50 in. for a complete revolution. Hence one division of the micro- 
meter screw represents 1/5000 in. 
By bending the long arm at the joint n the knife can be placed in 
position to cut specimens from 1/2 in. upwards. As the knife always 
Fig. 41. 
^noves in a plane parallel to that of the glass plate, the sections are of 
even thickness and are not wedge-shaped. 
For cutting frozen specimens or specimens imbedded in paraffin, the 
edge of the knife must be placed perpendicular to the direction of 
the motion. For this purpose a small blade, fig. 41, h , is used, and the 
1898 s 
