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 vpeight and size of the machine and especially to the cost. 

 The metal housing, just referred to. (inly partly protects the mechanism 

 from dust or other injury. This would he 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 

 notches on the wheel A and consequently the arc 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 C. just mentioned, a section 3 notches or 15 u is cut. Raising the 

 block B 3 mm. above the third mark just mentioned a section 4 notches 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 E 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 arc 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 arcs 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 C. with 

 paraffin or better with beeswax and then applying concentrated HNO3. 



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 ai'e 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 E 

 through a much greater arc and would allow sections of very much greater 

 thickness to be cut. A corresponding long graduated arc can then be at- 

 tached by a shouldered center to the post C which would control by means 

 of a movable arm the movements of the metal arm E to any desired de- 

 gree or extent and therefore still cut very thin or very thick sections. 



