ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
709 
When this has been worked through, the screw can be drawn back by 
the handle shown at 1 in fig. 105. 
The special table required for the microtome is seen in fig. 105. The 
lower mechanism is enclosed in a metal cover 2. At 3 is shown a band 
which can be attached to the screw z in fig. 104, and then stretched out 
above the table to the left, where it is adjusted near to the knife by the 
screws a and b (3 in fig. 105). At 4 is seen a wooden cover for the upper 
part of the instrument. At 5 and 6 are two smaller knife-holders, with 
corresponding object-holders at 8 or 9. At 7 are the small screw-heads 
which serve to adjust the screws //in fig. 104. 
The chief advantages offered by the instrument are as follows : — 
(1) The very great stability of all its parts. 
(2) Sections as large as 4 X 4 cm. can be easily prepared with it. 
(3) The limits of the cutting thickness lies between 0*5 and 40 
microns and 80 different thicknesses of section can be obtained. 
(4) The movement of the knife begins in all cases when the paraffin 
block is raised above it, and ends before the knife again begins to cut. 
(5) The length of the paraffin block can amount to 7 cm. and even 
more if necessary. 
(6) The paraffin block is freely movable in all directions and can be 
fixed in any position without altering the adjustment. 
With respect to the use of the instrument in preparing series of 
paraffin sections the author discusses the difficulties commonly met with. 
Of these the two most serious are — 
(1) The pressing together of the sections. 
(2) The slitting of the band along its length. 
The first difficulty was found to increase regularly with the angle 
between the faces forming the edge of the knife. 
The kind of grinding powder employed in sharpening the knife has 
great influence on the behaviour of the edge. The author divides such 
powders into two categories distinguished as “ sharp ” and “ polishing.” 
Emery is a type of a “ sharp ” powder. Sharpened with this the 
edge shows beneath the Microscope a number of sharp notches, and the 
fault of tearing the sections is very marked with such a knife for sections 
thicker than 5 /x. On the other hand there is very little pressing 
together of the sections even with the thinnest. Vienna lime can be 
taken as a type of a polishing powder. With this the knife shows under 
the Microscope a straight edge almost without notches. With such a 
blade no tearing of the band is to be feared, and the pressing together 
of the sections is unimportant for sections thicker than 5 /x, so that it 
can be recommended for all ordinary work. 
For very thin sections then, some sharpening material intermediate 
in properties between the two preceding is necessary. 
The author’s experiments with various materials have led him to the 
choice of the three following : — 
(1) Oxide of iron prepared by igniting the oxalate which has been 
precipitated from a hot solution of ammonium oxalate by ferrous sulphate. 
(2) Oxide of iron obtained by igniting the double sulphate of iron 
and ammonium. 
(3) Diamantine No. 1, the composition of which is unknown to the 
author. 
