96 PREPARATION AND MOUNTING 
cleaned in the ordinary way. Sometimes the balsam is 
dissolved in the chloroform without being first hardened; 
but this is only to render it more fluid, and so give the 
operator less chance of leaving bubbles in the finished slide, 
as, the thicker the medium is, the more difficult is it to get 
rid of these intruders. 
It has been before noticed that some have objected to 
chloroform and balsam, believing that it became clouded 
after a certain time. Perhaps this may be accounted for 
in part by the fact that almost all objects have a certain 
amount of dampness in them. Others are kept in some 
preservative liquid until the time of mounting, and these 
liquids generally contain certain salts (Chapter V.). If 
this dampness, as well as all traces of these salts, however 
small, are not totally removed—the former by drying, the 
latter by repeated washings—the addition of chloroform 
will render the balsam much more liable to cloudiness than 
when balsam alone was used. It may safely be affirmed that 
benzole will be found in all cases a more valuable solvent for 
Canada balsam than chloroform. 
This mode of employing the balsam, however, will not be 
always applicable, as chloroform acts upon some substances 
on which balsam alone does not. Some salts are even soluble 
in it, the crystals appearing after a few days or weeks, 
whereas in balsam alone they are quite permanent. Hx- 
perience is the only guide in some cases, whilst in others a 
little forethought will be all that is required. 
The particular methods used for certain objects may now 
be entered upon. Many of the Diatomacez and fossil 
Infusoria, as they are sometimes termed, are mounted dry, 
and cleaned in the way described in Chapter III. Others 
are almost always placed in balsam, except where they are 
intended to be used with the leberkuhn and dark back- 
ground, by which means some of them are beautifully shown. 
The usual way of mounting them in balsam is as follows :— 
Take a drop of the water containing them, place it upon 
the slide, and evaporate over the lamp, whilst with a needle 
