154 Proceedings of Indiana Academy of Science. 
plicated and cumbersome system of expensive adjustments these parts are 
often housed in by a metal enclosure. All this adds, as above stated, unnec- 
essarily to the weight and size of the machine and especially to the cost. 
The metal housing, just referred to, only partly protects the mechanism 
from dust or other injury. This would be as well or better affected by a 
cardboard cylinder or even by a properly made cloth hood such as is used 
to cover microscopes when not in use and which are left temporarily on a 
table in the laboratory. A light glass box can easily be made of plates of 
single strength glass held together at the angles and corners by strong 
adhesive tape. One of these I have made and used for years with entire 
satisfaction and whose cost of making was trivial. 
I marked a graduated scale on the post C to control the number of 
notehes on the wheel A and consequently the are through which it would 
be turned and therefore the thickness of the sections that would be cut. 
For example when the top of the brass block B was placed 52 mm. from 
the base of the post C the wheel A was turned one notch and a section 5 u 
was cut. Raising the block B 3.5 mm. more allows a section 2 notches or 
10 u thick to be cut. When the block B is raised 4.5 mm. above the second 
mark on ©, just mentioned, a section 5 notches or 15 u is cut. Raising the 
block B 3 mm. above the third mark just mentioned a section 4 notehes or 
20 u is cut and so on. As the lever E goes up and down it moves not in a 
small curve, as might be expected, but in a straight line. When, however, 
the lever FE strikes the arm D on the brass block B, Fig. 1 the lever E is 
turned the amount desired. This really is equivalent, in principle, to a 
small are being formed when the cogwheel O is turned as a result of the 
small divisions for adjustment on the post C. Each one of the small ares is 
very small at the periphery of the cogwheel A, especially when the brass 
block B is placed 52 mm. from the base of the post C which allows, as 
stated, a section only 5 u thick to be cut. Due to wear and especially to lost 
motion, the calculated positions and distances from each other that the 
adjustment marks on the post C should be placed for cutting the sections 
of different thicknesses did not quite correspond with those positions found 
by experiment. The variation, however, was not great and if all lost motion 
could be eliminated the calculated and experimental data would of course 
exactly coincide. The marks and figures on the post C are conveniently 
made with an etching tool or by covering the surface of the post ©, with 
paraftin or better with beeswax and then applying concentrated HNO,. 
Back of the cogwheel A, Fig. 1, were originally placed two lugs or pro- 
jections cast in or built in with other parts of the microtome here shown, 
Fig. 1. These are so placed as to limit the sections, as they could originally 
be cut, to a total thickness of 50 u. This is a much greater thickness than 
the majority of microtome sections are ordinarily cut. Occasionally, how- 
ever, it is desired to cut sections thicker than this and the arrangement 
just referred to above of thickness limitation of the sections is a decided 
inconvenience. This difficulty may be solved by removing the lugs or pro- 
jections above mentioned. This would then allow a sweep of the arm FE 
through a much greater are and would allow sections of very much greater 
thickness to be cut. <A corresponding long graduated are can then be at- 
tached by a shouldered center to the post C which would eontrol by means 
of a movable arm the movements of the metal arm Eto any desired de- 
gree or extent and therefore still cut very thin or very thick sections. 
