102 THE MICROSCOPE 



the mixture is not too hot when the stem is first dipped in ; it is 

 best to dip the stem in and withdraw it again for a minute, and 

 then finally plunge in and proceed as above. More of the paraf- 

 fin mixture is now poured in, until the specimen is thoroughly 

 imbedded. The whole is to be put away in a cold place for an 

 hour or so, when the mass will be firm enough to be cut with ease. 

 Sections may be made with a razor, kept constantly wetted with 

 water; or, if the preservation of colour be no object, methylated 

 spirit may be employed for the purpose. 



Embedding Agents. — Insects enclosed in chitinoiis cases may, 

 according to Hyatt, -^ be advantageously embedded in shellac. For 

 this purpose, the insect is to be placed in alcohol, and allowed to 

 remain there until it is thoroughly permeated by the spirit. It 

 must then be removed to a clear alcoholic solution of shellac, in 

 which it may remain for a day or two. A cylinder of soft wood is 

 now to be so prepared that it will fit accurately into the tube of 

 the microtome. This cylinder is now to be split longitudinally 

 down the middle, and a groove cut into one or both half-cyfinders 

 sufiiciently large to admit the object without pressure. The two 

 halves, with the object enclosed between them, are now to be 

 fastened together with thick shellac varnish, and a thread passed 

 around them to keep them in position. In a day or two the 

 shellac will become quite hard. The cylinder is then to be soaked 

 in warm water to soften the wood, then placed in the microtome, 

 when thin sections may readily be obtained from it. If the sec- 

 tions should be rendered so opaque by the presence of the shellac 

 as to interfere with their satisfactory examination, the addition 

 of a few drops of solution of borax will soon render them trans- 

 parent. 



Bleaching Vegetable Sections. — The agents most commonly 

 used for bleaching are : — (i) Alcohol ; (2) Solution of Chloride of 

 Lime ; (3) Labarraque's Solution of Chlorinated Soda, made by 

 decomposing Lime Chloride by the action of Sodium Carbonate. 

 There are, in certain cases, objections to these methods, and we 

 much prefer the plan recommended by Dr. Marsh, which is as 



* " American Monthly Microscopical Journal," 1880. 



