270 
COERESPONDENCE. 
delicate appearance of these wax backgrounds, nor can a cell be 
built up in any manner more readily. I use the sheets prepared 
for wax flowers, and of course colours may be selected to suit the 
object. The disks are punched by a solid plunger, which must 
frequently be cleaned by punching disks from a thick card either 
oiled or prepared with a little turpentine. Care will enable one 
to prepare these rapidly. 
Chloral Hydrate as a Medium for Mounting.— Mr. T. S. Ealph 
writes from Melbourne to ' Science Gossip ' of October, advocating 
this substance as a medium for mounting. He says that this chemical 
compound will dissolve and unite perfectly with many substances, 
and from some of its combinations we may obtain mediums which 
may vary from a fluid to a jelly-like or gum-like consistence. Chloral 
hydrate, besides uniting with gum and resins, also unites with alka- 
loids ; as salicinine, quinine, and cinchonine. " Place a small portion 
of chloral on a glass slide, add a little portion of water, and a nearly 
equal bulk of either of the above ; gently heat over a flame, mixing 
the two materials with a needle or glass rod : these will unite, and 
when cooled be found to be viscid and clear. To such a mixture 
camphor can be added, or glycerine. If a number of such experi- 
ments be conducted, the operator will soon find out what he is likely 
to obtain, and thus contrive a new medium suited to some objects. I 
propose the following : — Make a nearly saturated solution of chloral 
in water ; filter, and then add sulphate of cinchonine to near satura- 
tion, A portion of this combination is placed on a slide, heated 
slightly and allowed to cool. The object is then placed in it and the 
cover applied, which, however, requires to be cemented with gum 
solution, and then Bell's cement or Canada balsam. To this ' arti- 
ficial balsam,' as I am inclined to call it, I have added a little 
dextrine, so as to render it more solid. Your workers can make 
trial, and report on it. Glycerine and dextrine together boiled, and 
then chloral hydrate added, make a clear solution, which, I think, 
may be tried also." 
COKKESPONDENCE. 
Dr. Woodward's Photographs of Frustulia Saxonica. 
To the Editor of the ^Monthly Microscopical Journal.'' 
Wayland Depot, N.Y., August 11, 1876. 
Dear Sir, — I have this moment read your remarks in the August 
number on my note on " The Markings of Frustulia Saxonica " There 
are, of course, many things in the way of obtaining maximum per- 
formance. Perhaps my remark about careful adjustment, &c., may do 
Dr. Woodward an unintentional injustice. I do not wish to be under- 
stood as saying, nor do I think that Dr. Woodward has not a good 
glass and is not a skilful manipulator ; but every observer understands 
