GvYj on preserving Microscopic Objects in Tubes, 79 
scope from person to person among a class seated at a table,, 
or to make use of a cheaper instrument passed from hand to 
hand. Such a simple and cheap instrument I have been for 
some time in the habit of employing. A more expensive and 
complete instrument, with and without a light attached, has 
been since devised and successfully employed by my colleague. 
Professor Beale. In his instrument. Dr. Beale makes use of 
the ordinary microscopic slide ; but I have always preferred 
to use a disc of glass, or of card-board, ivory, bone, or wood, 
or rings of gutta percha turned off the tube. Such discs can 
be completely enclosed in the instrument, and may thus be 
rendered secure from accident or intentional displacement. I 
need not detain you by describing the mode of mounting the 
tubes on these discs. I send round specimens which will 
suffice, after the details I have already given. I may, how- 
ever, observe that the readiest mode of mounting the tubes 
for cursory examination is to warm the ends in the flame of 
the spirit-lamp, and drop the tube on to a ring of gutta percha. 
This ring, placed in an appropriate holder, can be put under 
the microscope and examined. 
Having now indicated some simple and obvious methods of 
mounting these small tubes, so as to be able to examine their 
contents under the microscope, I must next give some 
account of the mode of making the tubes themselves, of 
placing the objects within them, and of securing and pre- 
serving them. 
It will be understood that the tubes of which I am speak- 
ing are always of much smaller bore than the tubes or canes 
(as they are technically called) drawn in the glass-house. 
They must be the work of the glass-blower, and are made by 
melting the smaller sized tubes or canes in the flame of the 
lamp, and drawing them out. They can be made by any one, 
after a little practice, by using for the purpose a spirit-lamp 
with a large wick. They are best drawn out, several in suc- 
cession, from the same piece of tubing, and then divided into 
lengths by marking the tube with a file. Each portion of the 
tube so drawn out and divided assumes the shape of a long 
tube of uniform, or nearly uniform, minute bore, terminated 
at either end by a short tube of the size of the cane from 
which it was drawn. (I send round specimens of the tubing 
or cane,^^ as supplied by the glass-blower, of a portion of 
this tubing drawn out into two small tubes, and of a minute 
tube of the form I have described.) I may here state that 
though, for certain exceptional purposes, the chemist employs 
green, or German glass made without lead, for all other pur- 
poses the common white glass, containing the usual quantity 
VOL. X. ^ / 
