218 THE MICROSCOPE. 
It occurred to me that this cold-producing quality could be 
utilized in microscopy for the freezing of specimens for section cut- 
ting, and to learn its effect as compared with ether, a few experi- 
ments were undertaken. 
The instrument used was the ordinary one consisting of a thin, — 
metal stage arranged over a small chamber, to which air is ad- 
mitted by several perforations at its sides. The spray tube is in- 
serted into this chamber in such a manner that the ether is thrown 
against the under side of the stage, causing, by its evaporation, an 
intense cold. A small specimen, glued with gum arabic mucilage to 
the upper side of the stage was thus frozen by ether in five min- 
utes, and this sufficient for the cutting of thin sections. The 
Pictet fluid did the work on a like specimen in one and a half 
minutes. Aside from the rapid action of the latter, it had the ad- 
vantage of a more permanent effect, so that many more sections 
could be cut than when ether was used. 
In the above trial the Pictet fluid was applied by attaching 
a piece of rubber tubing to the mouth of the siphon, and this to a 
glass tube drawn somewhat to a point at the end. I found, how- 
ever, that the substage chamber of the freezing instrument was too 
open for the fluid, much of which bubbled out and was lost. This 
led me to devise a new arrangement, which was found to be not 
only far superior for the Pictet fluid, but for the ether as well. 
A large cork (see cut) of firm texture was obtained, and a 
square chamber, about one half inch in depth, was hollowed out at 
one end. (A.) A round opening was 
then bored, running from the center of 
one of the base lines of the chamber 
obliquely downwards and outwards, 
for the introduction of either spray 
or glass tube (c). On the other side 
of the chamber, though not directly 
opposite, a small hole (&.) was made 
to serve as a vent. The top was 
then covered with a thin piece of 
zinc plate, (B.) securely tacked on. The upper surface of the plate 
was then nicked, (not perforated) with the point of a knife blade, 
and the thing was done. If ether is used, some little saving can 
be accomplished by boring a hole from the bottom of the chamber 
