MOUNTING OBJECTS IN CANADA BALSAM. 309 



disappear entirely; but when winter approaches they will 

 reappear, and according to the amount of cold, so will the 

 vacuities increase in size. 



Fossil Infusoria, Sfc. — These, together with spicula of 

 sponges and objects of a siliceous nature, which have been 

 dissolved out by acid from a calcareous or other matrix, 

 may be very easily mounted in balsam without air bubbles by 

 pursuing the following plan : — If the objects be in fluid, a 

 small quantity of the sediment in which they are contained 

 may be taken up by one of the tubes shown at fig. 86, and 

 placed upon a number of slides, and each slide examined by 

 the microscope ; those containing good specimens should be 

 laid aside for mounting, whilst the others may be cleaned off. 

 If one of the slides fixed upon for mounting be held over the 

 lamp, the fluid will speedily evaporate and leave the objects 

 behind; whilst this is going on, the needle-point may be 

 used to stir and keep them from collecting together, and so 

 large a place should be made on the glass as not to exceed 

 the size of the thin glass cover; the objects must be all kept 

 as nearly as possible within this space, and not allowed to 

 get near the outer margin. Should many impurities be 

 present with the infusoria, they will be almost certain to col- 

 lect at the margin of the fluid as it evaporates, the cover in 

 these cases should be only so large as to reach nearly to the 

 margin, and the ring of impurities may be scraped away 

 after the cover is fixed on, the whole field being then left 

 perfectly clean. 



When all the fluid has evaporated, the balsam may be used 

 as follows : — A small drop having been placed upon the slide 

 on one side of the spot where the objects are, this is to be 

 heated until all air bubbles have disappeared; the slide is 

 then to be tilted to allow the balsam to run down over the 

 infusoria, the cover previously warmed is to be laid upon it 

 and pressed, and the object finished in the usual manner. 



When objects of a cellular nature have to be mounted, if 

 they be such that heat wiU not much injure, they may be 

 boiled in the balsam, otherwise numbers of air bubbles will be 

 left in the cells, and the true stracture cannot be satisfactorily 



