972 ` Mhe American Naturalist. [November, 
melted, though the water rapidly evaporates. The slides are kept 
there, with a cardboard cover over them to keep off dust, until the 
evaporation is complete and the sections adhere to the slide. 
The time required for this varies according to the thickness of the sec- 
tions; for thin sections one hour is generally sufficient for complete 
fixation, but the important point is that the paraffine must never be 
melted until the last trace of water has disappeared from the slide. 
melted until the last trace of water has disappeared from the slide. 
If this premature melting happens by any accident the sections are 
certain to peel off later. A few experiments enable one to be sure of 
the point when the slides are safe. 
After complete fixation the paraffine is melted by putting the slide 
inside the oven, then washed off with turpentine or xylol. 
One of the great advantages of this method is the perfect ease and 
safety with which it allows sections on the slide to be manipulated, so 
that the most various stains and reagents can be applied successively 
to a slide, e. g., the complicated processes used to demonstrate bacteria 
in the tissues can be applied, with the certainty, moreover, that there 
is nothing on the slide to be stained which was not in the section. 
A Method of Killing Nematodes for Microtome Sections. 
—Inquiries from several zoologists as to how Nematodes may be pre- 
vented from curling while being killed, leads me to publish the follow- 
ing very simple but satisfactory method. This method, so far as I 
know, was first used by my friend, Dr. Kaiser, in preparing Echino- 
rhynchus for the microtome, and I have now used it several years and 
find it indispensible in fixing Nematodes and other worms. 
A worm—only one can be killed at a time—is placed upon a large 
slide with a few drops of water; a second slide is placed over the worm 
and moved slowly to and fro. This movement causes the worm to 
straighten. As soon as the Nematode assumes the desired position the 
fixing liquid is pipetted between the slides, the motion of the upper 
slide being continued until the worm is dead. By this method one 
can obtain a specimen which is perfectly straight and round. If the 
worm is delicate, too much pressure must not be used during the rolling Y | 
process. Pressure may be avoided by pasting a piece of paper on the 
upper surface of the second slide and using that as a handle. 
As killing liquid I generally use the following solution: Corrosive : 
sublimate + alcohol 70% + a few drops of acetic acid heated to 
50° C., which passes through the cuticle very quickly.—C. W. 5. 
