OP 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 Is. 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 tho 

 syringe generally, if the piston should not then be readily 



