NOTES AND MEMORANDA. 
359 
salt mixture. The process was so tedious that a more expeditious 
method appeared desirable, and I therefore constructed an in- 
strument for freezing with ether spray, and described it in the 
‘ Journal of Anatomy and Physiology’ for April, 1877. At this time 
I was informed that an instrument was described by Mr. Hughes 
in the same journal twelve months previously ; but finding my 
microtome simpler in construction and more expeditious in freezing, 
I have employed it, with some slight modifications, up to tlie 
present time. The woodcut reju’esents 
in vertical section the freezing micro- 
tome which I constantly employ, and 
which I can very strongly recommend 
for general use. The lower half {a) 
is in principle an ordinary Stirling 
microtome ; the upj)er half consists 
of a freezing chamber (h) and the 
section plate (c). As regards the 
microtome, I always insist upon the 
use of an oval instead of a circular 
plug (g), whilst the screw should be 
three-quarters of an inch in diameter, 
finely worked, and with a milled head 
at least y of an inch wide. The 
freezing chamber (h) should have a 
false sloping bottom (/) leading to 
an exit tube (e^, which conducts off the condensed ether. Extremely 
simple as this contrivance appears, it is absolutely necessary for 
success that attention be paid to the following details of construc- 
tion. The freezing chamber consists of a large hollow cylinder 
of zinc, slightly over two inches in diameter, and capped with a 
plate of the same metal. This cylindrical chamber is soldered on 
to the microtome plug, so as to ensure absolute steadiuess in 
working, and it possesses three circular openings three-quarters of an 
inch in diameter, one placed in front of the two others laterally 
opposite each other. The section plate (c) is also made of zinc of 
an inch thick, and raised upon the vertical arm (d), also made of the 
same metal. The opening in the section plate should be sufficiently 
large to allow of the free play of the freezing chamber (h) through it 
without affording any point of contact between the two. With a 
freezing chamber such as the one described, beautifully large and 
thin sections may be obtained with ease. The material emi)loyed in 
the construction of the freezing chamber and section plate is a matter 
of importance, and I met with frequent failures and disappointments 
when endeavouring to utilize other more workable metals ; brass above 
all metals was found unsuitable, and zinc alone fulfilled all the 
requisite conditions. Theoretically, it was supposed that the metal 
chamber should be covered with a non-conducting material, such as 
felt, wood, &c., and that the conduction between the section plate and 
body of the microtome should in like manner be cut off ; but practically 
it was found that at the sacrifice of a small amount of ether rapid 
h 
