9O HOW TO WORK 



172. Size of the Particles of the Colouring Matter used. The 



size of the particles of the different substances employed in making 

 opaque injections is represented in pi. XXIV, and if the different 

 figures be compared with one another, it will be observed that those 

 colouring matters which have been recently prepared are in a much 

 more minute state of division than those which have been kept for 

 some time. The appearances represented were obtained by examina- 

 tion with a power of 2 1 5 diameters. 



Opaque injections are represented in pi. XXV, figs. 161, 162. 



173. Of Injecting Ditt'erent Systems of Vessels with Different 

 Opaque injections. It is often desirable to inject different systems of 

 vessels distributed to an organ with different colours, in order to ascer- 

 tain the arrangement of each set of vessels and their exact relation to 

 one another. A portion of the gall-bladder in which the veins have 

 been injected with white lead, and the arteries with vermilion, forms 

 a beautiful preparation. Each artery, even to its smallest ramifica- 

 tions, is seen to be accompanied by two small veins, one lying on 

 either side of it. A beautiful injection of the gall-bladder is repre- 

 sented in pi. XXV, fig. 1 6 1. 



In an injection of the liver, four sets of tubes may be injected 

 with the following different colouring matters : The artery with 

 Vermilion, the portal vein with White Lead, the duct with Prussian 

 Blue, and the hepatic vein with Lake. Many opaque colouring 

 matters besides those above-mentioned may be employed for double 

 injections. 



Of Transparent Injections. 



174. Advantages of Transparent Injections. For many years I 

 have abandoned the old plan of making injected preparations, in 

 favour of such transparent injecting fluids as are miscible with water 

 in all proportions. Besides the colouring matter these contain solu- 

 tions which exert a preservative action upon the tissue with which 

 they come in contact, or render certain elements of the tissue more 

 transparent or opaque. By this new plan of injection most important 

 advantages are gained, for not only are the vessels injected with 

 colouring matter, but 



1. The tissues are preserved from decomposition or change by 

 the action of the fluids of the body which are washed out by the 

 injection. 



2. Certain tissues may be rendered more distinct. 



3. Every structural element of the tissue can be seen as well as 

 the vessels. 



