OF MICROSCOPIC OBJECTS. 93 
time, a hot-water bath is sometimes made use of, which is 
simply a flat tin, or other metal case, with a mouth at the 
side, that when the hot water is introduced it may be closed 
up, and so retain its warmth for a long time. An excellent 
bath may be made of an ordinary water-plate—costing 
about 1s. 9d. This may be filled either with hot water or 
sand, and if to it be added a flat tin cover such as is used 
in eating-houses, costing about 6d.—a very effective oven 
for baking slides is the result. It may be placed on the 
hob, or over or near any source of heat. It is easy to add 
a thermometer if necessary. In working, the slide is laid 
upon it, and so admits of longer operations, when required, 
without growing cold. Sometimes a spirit-lamp is placed 
under it to keep up an equal heat through excessively long 
processes. Where the time required, however, is but short, 
a thick brass plate is sometimes used (see Chapter II.), 
which may be heated to any degree that is required, the slide 
being previously placed upon it. 
Some objects, which are so thin that they are usually 
floated upon the slide, as before stated, require no steeping 
in turpentine or other liquid. These are best mounted by 
covering with a little diluted balsam, and after this has had 
time to penetrate the substance, ordinary balsam is laid 
upon it, and the slide finished in the usual manner, 
I have stated that balsam is usually applied to the slide 
and objects with a bluntly-pointed glass rod; but for the 
purpose of drawing the balsam from the bottle, and convey- 
ing it to the desired place, Dr. Carpenter uses a glass 
syringe with a free opening. These are his instructions :-— 
“This (the syringe) is most readily filled with balsam, in 
the first instance, by drawing out the piston, and pouring 
in balsam previously rendered more liquid by gentle warmth; 
and nothing else is required to enable the operator at any 
time to expel precisely the amount of balsam he may require, 
than to warm the point of the syringe, if the balsam should 
have hardened in it, and to apply a very gentle heat to the 
syringe generally, if the piston should not then be readily 
