INTRODUCTORY. 



The brittleness is, however, sometimes very helpful in 

 minute dissections. Another property of clove oil is that it 

 does not easily spread itself over the surface of a slide, but 

 has a tendency to form very convex drops, and this also 

 makes it frequently a very convenient medium for making 

 minute dissections in. 



If it be desired to dissect in a watery fluid, such as 

 glycerin, it may be well to prepare the slide by spreading on 

 it a thin layer of MAYER'S albumen, and on this place a 

 small drop of glycerin, or other dissecting medium. As soon 

 as the dissection has been accomplished, a cover may be let 

 fall, horizontally, on to the preparation to keep the parts 

 in place, and a weight placed on it. Then the mount may 

 be filled up with glycerin, or other mounting medium, run in 

 under the cover, and closed, if desired, or instead of the 

 albumen a solution of gelatin may be taken, and hardened 

 in formol with the objects on it. For a balsam mount, after 

 clove or cedar oil, SCHALLIBAUM'S collodion may be taken, 

 and the organs fixed in situ on this by adding xylol. 



10. Instruments. For all that concerns the mechanism and 

 manipulation of the Microscope, see vol. i of CARPENTER'S The 

 Microscope, eighth edition, 1891 ; paying particular attention 

 to all that is said concerning the .English and the Continental 

 Models, pp. 254 to 26 J, the Substage, pp. 184 to 189, Con- 

 denses, pp. 289 to 316, and Tube Length, pp. 158 to 159. 



For information concerning the principles of construction 

 and manipulation of the Microtome, see also CARPENTER'S 

 Tim Microscope. Microtomes are instruments for the 

 accurate production of thin slices of tissues. They are used 

 both for cutting tissues that have acquired a certain favour- 

 able consistency through having been imbedded in paraffin, 

 and also for cutting tissues that have been imbedded 

 in softer masses, such as collodion, and tissues that have not 

 been imbedded at all. Not all microtomes are equally well 

 adapted for all these three classes of work. The microtome 

 of the zoologist should at all events be one that is well 

 adapted for cutting imbedded material. 



Now there are two methods of imbedding in general use 

 the paraffin method and the celloidin method. In the 

 pnraffin method the object is cut dry, frequently with the 



