158 



THE VASCULAR SYSTEM 



and in a morphinised and curarised dog : 



In the uncurarised animal the convulsive movements of res- 

 piration by compressing the abdominal vessels raise the vena cava 

 and lessen the fall of aortic pressure. 



Similarly in Cohnheim's classical experiments, when he injected 

 oil into the pericardium to study the effect of impeding the filling 

 of the heart, there resulted no equality of residual pressures in the 

 aorta and vena cava. 



It has been supposed that a general constriction of the arterioles, 

 such as may be produced by the injection of adrenalin, would by 

 reducing the capacity of the vascular system raise the " mean 

 hydrostatic pressure," and therefore the capillary pressure. The 

 writer produced by injecting adrenalin a rise of arterial pressure 

 from 80 to 180 mm. Hg, and then arrested the circulation by 

 clamping the ascending aorta. The vena cava pressure fell to the 

 same residual pressure as when the aorta was clamped before the 

 injection of the adrenalin. A rise of pressure of 1500 mm. of blood 

 in the aorta may be accompanied only by a rise of 50 mm. in the 

 venae cava3, and this small rise is due not to diminution of the total 

 capacity of the vascular system, but to a greater return to the 

 vena? cava3 of blood squeezed from the splanchnic area and the 

 failure of the heart to empty itself in the face of the high resistance. 



It has been supposed that the intravenous injection of physio- 

 logical saline, or the injection of concentrated sugar solution this 

 produces hydrsemia by drawing water out of the tissues into the 

 blood it has been supposed that either of these agents increases 



