124 PHILOSOPHY OF ZOOLOGY. 



so fluid, as to render the examination extremely difficult. 

 Where the contained fluid is of an albuminous nature, as 

 in the ordinary circulating fluids, its coagulation is easily 

 effected by alcohol or vinegar. Sometimes sudden immer- 

 sion in boiling water is more convenient. Where the con- 

 tents of the vessel are chiefly gelatine, as in the dorsal ves- 

 sel of insects, tannin has been successfully employed in its 

 coagulation, 



3. Injection. Although the veins are found filled, af- 

 ter death, with the blood of the animal, which, by being 

 coagulated, enables us readily to trace their course, yet the 

 arteries are frequently in an empty state. It is usual to inject 

 these and other empty vessels, with air from a blowpipe or 

 glass tube, by which their dimensions and distributions are 

 more distinctly displayed. Instead of air, water is some- 

 times used, either in its natural state, or charged with glue, 

 which gelatinises upon cooling, or with different colours, 

 to point out more clearly the direction of the different parts. 

 Quicksilver is likewise frequently employed, where the 

 coats of the vessels are of sufficient strength to resist its 

 weight. Another kind of injection is formed, of a mixture 

 of bees-wax, resin, turpentine, and colouring matter, which, 

 when cold, is sufficiently firm to exhibit the ramifications 

 of the vessels in their natural position *. In some cases, 

 the exterior vessels are corroded by diluted nitric acid, for 

 the purpose of exhibiting more distinctly the wax casts of 

 their interior. The cavities of the bones of the ear, of 



* Those who wish to become acquainted with the art of injecting, and 

 preparing the organs of animals, may consult, with advantage, " The Ana- 

 tomical Instructor," by Thomas Pole, 12mo, London 1813. 



