Regulalhuj the Thivkness of Microloiiic i^ections. 153 



block out carrying lli(> spccinicii to ilic soctioiiiiif,' knife. The threaded 

 shaft's diameter is r> iiini. and its circuiiirereiico in.TOSO mm. The circum- 

 ference of the wheel is therefore 1". times that of tlic shaft. Since tliere 

 are 100 notches in the circumference of the wheel the shaft turns .in mm. 

 jier notch or 1.^0 n. TJie shaft is threaded with 20 threads to 1 cm. and 

 therefore one thread or revolution or the 100 notches eiiuals ~, mm. or 

 ."iOO u that the .section is moved out. Therefore when the larse cogwheel is 

 turned one notch tlu< parallin block carryin.i; the specimen is moved out so 

 that a section 5 u. thick will be cut. The above mentioned points make it 

 clear that a faulty .spring .system for a machine cuttinjr such thin sections 

 would be serious for even rather thick sections and especially so for very 

 thin ones. 



My improvement is the use of a brass block (F. Fig. 1 ) attached to post 

 (\ This post was originally in the machine and carries at the top a metal 

 arm D so arranged as to arrest the movement upward of a lever E attached 

 to the brass cogwheel A above referred to. The metal arm E projects :].'> 

 cm. beyond the circumference of the brass cogwheel A and carries a ratchet 

 Ct. which turns A as the siiecimen is raised above the sectioning knife. The 

 brass block 15 attached to C, for regulating the thickness of the microtome 

 sections, is made of solid brass. It is 35 mm. long and 21 mm. wide on the 

 upper side, Fig. 2. In Fig. 2 A is the path of the post C through B ; B is 

 the insert plate. F. the set screw and D the set screw for the brass block B. 

 The block B is 25 mm. high, 23 mm. long and 21 mm. wide at the shoulder 

 where the set screw I), is placed Fig. 2. The part projecting above the set 

 screw D which tightens the block B on the post C is 11 mm. thick, Fig. 2. 

 This part which is just above the set screw I have cut out so as to allow 

 an insert plate i\ Figs. 2 & 3, to be used. This I made from a steel plate 

 which covers the bobbins of a sewing machine and cut th(> brass block as 

 illustrated so that its sides had the same angles as the steel plate and al- 

 lowed the latter to slide true in the channel cut Fig. 2 c. This steel insert 

 plate is in cross section 14.5 mm. at the base. 13 mm. at the top and 21 mm. 

 long, C. Fig. 2 & 3. The illustrations C Fig. 2 & 3 represent the exact size. 

 The block has a hole 12.5 mm. in diameter bored vertically through it at 

 one end of the insert plate. A, Fig. 2 & 3, so that the post C, Fig. 1, can he 

 passed through it. and on which it can be moved up or down to the desired 

 position. In case of wear on the brass lever E a new brass tip can be used. 

 In fact it can he grooved and short new insert plates used there as at C. 

 Fig. 2 & 3 on the lower side of E at the striking point. I made use here 

 of the principle that hard and soft metal surfaces where wear is present 

 should be brought together so that any wear will take place on the soft 

 metal which can be replaced. This principle is used generally in machin- 

 ery. Since the metal arm E strikes the insert plate with a sort of shearing 

 stroke in descending it has a tendency to push the insert out of place. . This 

 I have remedied by putting a set screw B, Figs. 2 & .3. through the insert 

 plate C and into the brass block B. Fig. 2. This is not shown in the photo- 

 graph but is shown in the drawings of the brass block. Fig. 2. Figure 2 is a 

 drawing of the brass block above mentioned which I constructed for this 

 imrpose. It carries on its upper .side, where the lever strikes, the insert 

 plate above described. :Many of the later types of microtomes of the kind 

 here illustrated are even much more complicated. In addition to a com- 



