ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 207 
it produces sections all parts of which are in one plane. The sections 
can also be obtained at a greater rate of speed, and the inclination of the 
knife can be changed at will. One disadvantage of the instruments lies 
in the swallowtail grooves of the slide-ways which are not so accurate 
as those of the rocking microtome. The instrument can bo used for all 
kinds of paraffin sections for normal, pathological histology, and series 
of embryonic sections. For moist and frozen sections it is naturally not 
adapted. 
A Bacteriological Potato Section Cutter.* — Dr. C. F. Dawson 
describes his apparatus thus : — “ Several methods of preparing potatoes 
for a culture medium are now in vogue, each having more or less effi- 
ciency, and a variable amount of labour. 
One of the most common methods is the use of a large cork-borer, 
or apple-corer, to cut a cylinder from the potato. This cylinder of 
potato is divided diagonally, thus making two preparations. Pieces of 
glass tubing are inserted into the thick ends of the two pieces of potato, 
and they are placed into ordinary test-tubes and sterilized. The pieces of 
glass tubing serve to support the potatoes above the level of the con- 
densation water, which always settles into the bottom of the tube. In 
some instances, specially made culture-tubes having a constriction near 
the bottom of the tube, are used. The constriction supports the potato, 
and the condensation water falls into the reservoir thus formed in the 
bottom of the culture-tube. 
If the potato medium is to be kept for some time, we find that there 
is a great change in the form of the potato, due to evaporation of water 
from it. The inoculation surface becomes irregularly concave, the thin 
end becomes dry and curls, and the preparation presents an unsightly 
appearance. When the potato cultures are to be used for exhibition 
purposes it is desirable to have them present a neat appearance. The 
aim of the writer is to describe an apparatus which he has devised to 
prevent the changes in form referred to. The apparatus consists of two 
pieces: a plugger represented by fig. 34, and a curved knife represented 
by fig. 35. The plugger is made from a metal tube about six inches long, 
and of a diameter a little less than the culture-tubes to be used. The side 
of the metal tube is cut out by sawing slantingly through the wall and 
across the inner diameter of the tube to the opposite wall at such an angle 
that the distance traversed by the saw will be about two inches and then 
by sawing vertically across the diameter of the tube to the wall of the 
opposite side. The end of the tube nearest the side opening is sharpened 
from the outer surface, and a wooden handle is fitted into the other end. 
The curved knife (fig. 35) is used to cut a convex surface on the 
potato section so as to compensate for the loss by shrinkage from evapora- 
tion. After a time this convex surface will become nearly flat, whereas, 
if the surface were cut flat at the outset, it would now be irregularly 
concave. 
This knife is made by cutting out a segment of a circular tube of 
about 1^ in. in diameter, the segment having continuous with it a narrow 
portion of the wall of the same tube, which portion serves as a handle. 
The segmental portion is sharpened upon its convex surface. 
* Amer. Mon. Micr. Journ., xiii. (1892) pp. 243-4. 
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