PECULIARITIES OF BLOOD SUPPLY IN CERTAIN VISCERA 255 



ume of such viscera as the liver and kidneys. The same changes will 

 obviously also supervene when there is regurgitation of blood from the 

 left ventricle to the left auricle, as in cases of mitral insufficiency. 



CIRCULATION THROUGH THE LIVER 



.The liver is the only gland in the body receiving both venous and 

 arterial blood, the former being supplied to it at a very low pressure 

 by way of the capacious portal vein, and the latter at very high pressure 

 by the strikingly narrow hepatic artery. Except for the relatively 

 small amount of blood which is supplied to the walls of the blood vessels 

 and the biliary ducts, none of the hepatic artery blood mixes with that of 

 the portal vein until the vessels enter the hepatic lobules. Beyond this 

 point the two blood streams mix and the combined stream is drained 

 away by the sublobular and hepatic veins. 



Methods of Investigation 



To study the relative importance of these two sources of blood sup- 

 ply, and also to investigate the manner in which the latter is controlled, 

 the most satisfactory method has consisted in measurements of changes 

 in volume flow rather than in those of changes in pressure. The vol- 

 ume-flow measurement has been made either by connecting stromuhrs 

 (page 207) to the hepatic artery or portal vein, or by measuring the out- 

 flow of blood from the hepatic vein into the vena cava, first with both 

 inflow vessels intact, and then with one of them ligated. An objec- 

 tion to the first (the stromuhr) method is the possible interference with 

 bloodflow or blood pressure produced by inserting the stromuhr into 

 the entering vessels, and also the fact that simultaneous measurement 

 of the flow in both vessels can not be made satisfactorily. 



To measure the outflow from the hepatic veins, the aorta is ligated 

 below the celiac axis and a wide cannula is inserted into the central 

 end of the vena cava below the level of the liver, a loose thread being 

 placed around this vessel just above the diaphragm. By pulling on this 

 thread the vena cava becomes obliterated, and the blood from the 

 hepatic veins is therefore diverted into the cannula, through which it 

 flows into one end of a vessel shaped somewhat like a sputum cup (the 

 receiver), the other end being connected by tubing with a piston re- 

 corder, from the movement of which the volume of blood flowing into 

 the receiver can readily be computed. To measure the flow of blood, 

 a clip on the tube of the receiver is removed af the same moment that 

 the thread around the vena cava above the diaphragm is tightened, 

 and when the receiver has filled with blood, this thread is again loosened 



