The Distribution of Blood in Shock. 195 



of portal venous pressure showed a diminution of the volume of the 

 intestines. In other words, the volume of the intestines during 

 shock varied directly with arterial blood pressure, irrespective of 

 increase or decrease in the portal venous pressure. 



This, so to speak, inverse relation of the volume of the intestine 

 can only be explained by recognizing that under such conditions 

 of lowered blood pressure so little blood is supplied by the arterial 

 side of the circulation that the effect of still further cutting down 

 the arterial supply produces a greater effect upon the volume of the 

 gut than the increased intravenous pressure. It must mean that 

 the combined sectional area of the arterioles is already small. 



These results confirm by another method of experimentation 

 the conclusions of Mann, and of Morison and Hooker, and the 

 failure in shock of venopressor mechanism, previously described 

 by Henderson. Although we do not agree with Henderson's 

 explanation of the cause of the failure of the venopressor mechan- 

 ism, yet we entirely agree with the importance which he has 

 ascribed to this mechanism. Our own experiments not only 

 confirm the failure of the venopressor mechanism in shock but 

 indicate the extent of this failure and the factors upon which it 

 depends. We can see no other factor which can be responsible 

 for the continued fall of blood pressure, after the period of partial 

 occlusion of the inferior vena cava, than merely the effect of the 

 mechanical distention of increased intravascular pressure upon 

 the capillaries and small venules of regions draining into the 

 inferior vena cava, and believe that this conclusion is emphasized 

 by the comparatively high level to which the arterial blood pressure 

 returns after the release of the ligature. 



Of all parts of the vascular system, the capillaries and small 

 venules are least capable of resisting the effects of increased 

 intravascular pressure. The combined sectional area of the 

 capillaries is very much greater than that of either the arterioles 

 or the venules. Any increase in the capillary bed, even to a small 

 extent, must, therefore, profoundly affect the general blood 

 pressure. It is certain that during the period of occlusion of the 

 vena cava the low blood pressure is due to the retention of blood 

 within these vessels. In our experiments there is certainly no 

 special sequestration in the vessels of the small intestine. The 



