74 HOW TO USE THE MICROSCOPE 



quantity ; but if they are mixed up with the object 

 it may be necessary to heat the shde on the table 

 until the balsam boils, and at that stage apply 

 gentle pressure on the cover. Such a proceeding, 

 however, requires great care ; with some objects it 

 would be disastrous. 



Another method is to first embed the object in 

 balsam on the cover-glass, set aside for twelve hours 

 under cover to keep dust off, then apply a fresh 

 drop of balsam, and finally lay the cover with 

 attached object on a previously warmed slip, taking 

 care to avoid bubbles, and seeing that the cover is 

 evenly laid and centred. 



Many writers advise gradual lowering of the 

 cover-glass from one edge with the aid of a needle, 

 but my own experience points to placing the cover 

 horizoiitally on to the balsam right off as the better 

 method. Let the reader understand that in this 

 work, as in all else, " Practice makes perfect " ; he 

 will improve his results with experience, and the 

 best remedy I can offer for difficulties that crop 

 up by the way is a blend of common sense with 

 patience. 



However convenient it may be to practise mount- 

 ing bought objects already prepared, it is surely 

 more satisfactory to do one's own preparing. Of 

 course the work of preparation varies with the 

 nature of the objects, but, by way of example, let 

 us suppose that we desire to mount a specimen of 

 the common flea. First we kill our object by im- 

 mersing it in methylated spirit, and we keep it in 

 the spirit until we are ready to go on with our work. 

 Being ready to proceed, we soak the object in two 



