~s 
Regulating the Thickness of Microtome Sections. 153 
block out carrying the specimen to the sectioning knife. The threaded 
shaft’s diameter is 5 mm. and its circumference 15.7080 mm. The circum- 
ference of the wheel is therefore 15 times that of the shaft. Since there 
are 100 notches in the circumference of the wheel the shaft turns .15 mm. 
per notch or 150 u. The shaft is threaded with 20 threads to 1 cm. and 
therefore one thread or reyolution or the 100 notches equals .5 mm. or 
500 u that the section is moved out. Therefore when the large cogwheel is 
turned one notch the paraffin block carrying 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 cutting such thin sections 
would be serious for eyen rather thick sections and especially so for very 
thin ones. 
My improvement is the use of a brass block (B Fig. 1) attached to post 
C. 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 3.5 
em. beyond the circumference of the brass cogwheel A and carries a ratchet 
G. which turns A as the specimen is raised above the sectioning knife. The 
brass block B 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, B 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 mim. wide at the shoulder 
where the set screw D. 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 C, Figs. 2 & 3, to be used. This I made from a steel plate 
which covers the bobbins of a sewing machine and cut the 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 ¢. 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 yertically through it at 
one end of the insert plate, A, Fig: 2 & 3. so that the post C, Fig. 1, can be 
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 be 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 
purpose. 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- 
