26 The Microscope. 



nifying power and the mode of illumination which 

 suit it, the latter particulars being given in some easily 

 understood abbreviations. 



The Canada balsam method involves more diffi- 

 culty, and is most fully described both by Dr. 

 Carpenter and Mr. Quekett, as well as in almost 

 all works on the microscope. The balsam (which 

 is a very pure turpentine) is placed warm on the 

 slide, and the object is completely immersed in it. 

 The glass cover is then put on, and in time, some- 

 times in a few hours, the balsam becomes quite hard, 

 and the object remains fixed 'and bright, as a fly in 

 amber. This method of mounting has many advan- 

 tages : it adds greatly to the transparency of objects, 

 thus allowing the details of their structure to be 

 clearly seen, and it preserves them better than the 

 dry method. Being a very " sticky " substance, it 

 should be used in a careful and methodical manner. 

 It ought to be kept in a wide-mouthed bottle, with 

 a tall hollow stopper, like the bottles for gum, but 

 instead of a brush there should be a glass rod, not 

 fastened to the stopper, but projecting into it, while 

 its lower end stands in the balsam. With this rod a 

 single drop of the balsam is neatly placed on the slide, 

 which is held over a spirit-lamp or laid on a tin vessel 

 filled with boiling water. The great difficulty about 

 mounting in balsam consists in the trouble caused by 

 air-bubbles appearing in it. When the drop is placed 

 on the slide, a few of these bubbles may appear, but 

 presently burst from the warmth; but no sooner is the 

 object well sunk into it than a host of small bubbles 



