OF MICROSCOPIC OBJECTS. 105 



pose of obtaining good polished sections of soft crystals, especially 

 of those easily soluble in water. 



" The nitre is thus polished on both its surfaces, which should 

 be brought as near as possible to parallelism." 



Some sections of the naturally formed crystals also show the 

 " rings " very well, as Iceland Spar, which gives a single ring 

 and cross ; but the difficulty of cutting and polishing them is 

 almost too great for the amateur, and must be left to the lapi- 

 dary. This curious phenomenon, however, may be seen by using 

 a plate of ice uninterruptedly formed of about one inch in thick- 

 ness. 



Before concluding these remarks on sections, I must mention 

 a few difficulties which may be met with, and their remedies. 

 The foremost of these is the softness of some objects, which have 

 not resistance enough in themselves to bear cutting even with the 

 sharpest instruments. This may often be removed by soaking in 

 a solution of gum, and then drying, which will render the sub- 

 stance firm enough to be cut, when the sections must be steeped 

 in water, and the gum thus got rid of. Small seeds, &c., may be 

 placed in wax when warmed, and will be held firmly enough when 

 it is again cold to allow of them being cut into sections, &c. 

 And, lastly, where a substitute for a microscopist's hand-vice is 

 required, a cork which fits any tube large enough may be taken 

 and split, the object being then placed between the two parts, 

 and the cork thrust into the tube, a sufficient degree of firmness 

 will be obtained to resist any necessary cutting, &c. 



DISSECTION. As I stated at the commencement of this chapter, 

 no written instructions can enable any student to become an adept 

 in this branch without much experience and no little study. I 

 will, however, describe the necessary apparatus, and afterwards 

 mention the mode of treatment which certain objects require. 



A different microscope is manufactured for the purpose of dis- 

 section, most first-rate makers having their own model. The 

 object-glasses of many of these are simple, and consequently not 

 expensive ; but one of the great requisites is a stage large enough 

 to hold the trough, in which the operation is often performed. 

 Where this is the case it would scarcely be worth the expense of 

 getting a dissecting microscope if the student were pursuing no 



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