GENERAL TECHNIC 27 



in the usual way. Sections of injected material are usually cut rather 

 thick, that the vessels may be traced the greater distance. 



Better results are frequently obtained by injecting separate 

 organs. This is accomplished by injecting through the main artery 

 of the organ {e.g., the lungs through the pulmonary, the kidney 

 through the renal). The injection is best done with the organ in situ, 

 although it may be accomplished after the organ has been removed. 

 The method is the same as given above for injecting an animal in toto. 



The so-called double injection by means of which an attempt is 

 made to fill the arteries with an injection mass of one color (red), 

 while the veins are filled with an injection mass of another color 

 (blue), often gives pretty, but usually inaccurate pictures, it being, 

 as a rule, impossible to confine each injection mass to one system. 

 Double injection is accomplished by first washing out the vessels 

 with normal saline and then connecting the artery with the red gelatin, 

 the vein with the blue gelatin, and injecting both at the same time, 

 the pressure driving the saline out of the vessels into the tissues. 

 The difiiculty is that either the arterial injection carries over into 

 the veins, or the venous injection carries over into the arteries. A 

 somewhat more accurate method is first to inject the veins with an 

 injection mass in which the coloring matter is in the form of granules 

 too large to pass through the capillaries, and then to inject the arter- 

 ies and capillaries in the usual manner. This method is especially 

 useful in demonstrating the vessels of the kidney, liver, and gastro- 

 intestinal canal. 



