MOUNTING OBJECTS. 215 



little cork nipple comes down with considerable force upon 

 the glass cover. In mounting algae, &c. with a gelatine 

 medium, the specimen should 

 he placed on the glass slide 

 with a small quantity of water, 

 and when properly arranged, 

 the thin glass cover must he 

 carefully put on, and a suffi- 

 cient quantity of gelatine me- 

 dium placed by its side ; gentle 

 heat should be applied to drive ^^^l^^XS^^ 

 out the water, when the gela- 

 tine flows under to take its place ; then put the object 

 aside to dry and harden. 



General Directions for the Preparation and Mounting 

 of Objects. — The objects exhibited by the microscope are 

 either opaque or transparent. The former, in the majority 

 of instances, require little or no preparation beyond placing 

 them in such a position as to show their external surface 

 by reflected or condensed light, and covering with thin glass to 

 exclude dust. Those objects, however, which it is intended 

 to examine by transmitted light require, in most cases, to 

 be prepared previously to mounting them, in whatevei 

 vehicle may be found most suitable for exhibiting then 

 structure. The medium most used for mounting trans 

 parent objects is Canada balsam. The pure balsam is, 

 however, too thick for use, and it requires to be diluted 

 with spirit of turpentine to render it sufficiently fluid to 

 permeate the structure to be exhibited. As a general rule, 

 it should be just fluid enough to drop readily from the 

 point of a needle. Those who desire to avoid the trouble 

 of mixing their own mounting medium, can procure it 

 ready for use from any of the microscope makers. There 

 are some few objects whose structure is so transparent 

 that they must be mounted dry. Scales from the wings 

 of butterflies and moths, of the podura and lepisma sac- 

 charina, and some of the diatomaceae are of this class. All 

 that is necessary in preparing objects for dry mounting, 

 is to take care that they are free from extraneous matter, 

 and to fix them permanently in that position in which 

 their structure will show to the best advantage. Care 



