MODERN METHODS OF EXAMINATION. 65 



Sometimes the syringe is substituted by a self-acting 

 apparatus, consisting of a Wolfe's bottle, containing the 

 fluid, which is pressed upon by a column of air from 

 another source, and driven through a flexible tube to the 

 pipe in the bloodvessel. 



The older anatomists used colored plaster or wax to 

 demonstrate the arteries and veins, but modern histology 

 requires finer materials. Isinglass or gelatin, colored, and 

 injected warm, or a solution of colored glycerin, are now 

 resorted to. The former serves for opaque, and the latter 

 for fine, transparent injections. 



The art of injecting can only be learned by practice, 

 yet perseverance, in despite of many failures, will insure 

 success. 



The liver, kidney, etc., may be injected separately, and 

 it is often desirable to use various colors for the different 

 sets of vessels. After injection thin slices may be cut off 

 and mounted in fluid or balsam. 



Preparation in Viscid Media. Dr. Beale has proposed a 

 method of preparing animal and vegetable tissues for ex- 

 amination with the very highest powers, which has led to 

 valuable results. It consists in using pure glycerin or 

 strong syrup, instead of watery solutions. In this way 

 an amount of, pressure may be applied to sections, in order 

 to render them thin enough for examination, which would 

 be destructive to specimens in water, while the preserva- 

 tive action of the media prevents change in the structure. 

 It is necessary to soak the specimen some time, and the 

 strength of the fluid should be gradually increased until 

 the tissue is permeated by the strongest that can be ob- 

 tained. Dr. Beale has found that minute dissection is 

 much more readily performed in such fluids, and that 

 even very hard textures, as bone and teeth, may be softened 

 by them, especially if acetic acid is added, so as to permit 

 thin sections to be made with a knife. He recommends 



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