OF MICROSCOPIC OBJECTS. 141 



must be examined from time to time to ascertain whether 

 the necessary degree of thinness has been reached. When 

 this is the case the section should be washed thoroughly and 

 dried. It must then be covered, which is best done by using 

 ordinary Canada balsam, as recommended in Chapter IV. ; 

 or, if the section is to be mounted dry, it must be freed from 

 balsam by washing, or soaking if necessary, in turpentine or 

 other solvents. 



Sections of some exquisitely beautiful objects are cut with 

 much less trouble than the above. The Orbitolite, for 

 instance, may be prepared in this manner. Take the object 

 and by pressure with the finger rub the side upon a flat and 

 smooth sharpening stone with water until the portion is 

 reached which it is wished to show. The strength of the 

 object will easily allow this to be accomplished with ordinary 

 care. This side may then be attached to the glass slide 

 with heated balsam, as above described, and the object may 

 then be gently rubbed down to the degree of thinness re- 

 quired to show it to the best advantage. After removing 

 all disengaged matter from the object by washing and 

 thoroughly drying, it may be mounted in balsam in the 

 usual manner, when it is equally beautiful as a transparent 

 or opaque object. From this it will be seen that in many 

 instances where a smooth stone is found sufficient for the 

 work (which is often the case when the section is mounted 

 in balsam) the final process of polishing advised above my 

 be dispensed with, as in the Orbitolite, Nummulite, &c., c. 

 It is quite necessary that the stones on which the objects 

 are rubbed be perfectly flat^ otherwise one side must be 

 acted upon before the other, and it will be found impos- 

 sible to attain anything like uniformity. Where it is not 

 practicable to cut a^ section, and the object is very thick, a 

 coarse stone may be* first used to reduce it and the smoother 

 afterwards. 



The consideration of the cutting of sections from shells 

 would scarcely be deemed complete without some mention of 

 what Dr. Carpenter terms the decalcifying process. Muriatic 



