PROCURING OBJECTS. 47 



is to drop on a small quantity of castor-oil that which has been filtered 

 cold must be employed, as otherwise it is liable to the same objection 

 as olive-oil ; and care must be taken that it covers the whole of the 

 salt, and has displaced all the particles of atmospheric air that may 

 have been adhering to the crystals. This having been done, a small 

 piece of very thin glass is to be carefully placed on the surface of the 

 oil, and any excess which may by this means have been pressed out 

 cautiously removed by bibulous paper from the edges. The margin 

 may then be covered by a coating of marine glue, a strong varnish ot 

 shellac or gold-size, and the crystals are permanently preserved for 

 observation. If varnish be used, one layer of it should be allowed 

 to dry for twenty-four hours, before the next is applied ; and during 

 this time, the slides must be maintained in a flat position. 



CHAPTER V. 



MICROSCOPIC OBJECTS AND MEANS OF 

 PROCURING THEM. 



43. I have already observed, that every department of nature is 

 full of objects of the greatest interest, when examined beneath the 

 microscope. To all these it is impossible even to allude ; but it is my 

 intention, in this section of the work, to refer to some of the more 

 interesting classes of objects, and the method in which they may be 

 obtained and prepared for examination ; thus, in fact, giving a kind 

 of outline of the extent of the use of the microscope. 



44. BOTANICAL OBJECTS. The elementary organs of plants 

 require the assistance of the microscope to render them apparent. 

 The forms of the .elementary organs of plants are, 1, Cellular tissue ; 

 2, Woody fibre, and 3, Vascular tissue. Cellular tissue composes the 

 pith and soft parts of plants, and consists of distinct vesicles of 

 various forms cohering together. Sections of the calycanthus florid us, 



