AND BLOOD PRESSURE 157 



another factor being the alteration of tissue metabolism produced 

 by the impeded blood flow with consequent want of oxygen, setting 

 free of crystalloids from colloidal combination, and increase of 

 waste products, leading to a rise of osmotic pressure and swelling 

 of the tissues. 



In the case of such an organ as the liver a great expansion 

 takes place when the outflow from the vena cava inferior is impeded, 

 or excess of blood or saline is injected intravenously. Here again 

 increase of surface exposure and stagnation of flow are the factors 

 at work which produce the greater outflow of lymph not the 

 increased capillary pressure. That the capillary pressure is in- 

 creased in such capsulated organs as the kidney, salivary gland, 

 liver, and brain when the outflow of venous blood (or secretion) 

 is impeded is proved by the increased tension of the organ, but this 

 increase must be uniform throughout each lobule, if not through- 

 out the whole organ, and cannot act as a filtering agent. 



THE RESIDUAL VASCULAR PRESSURE IN THE DEAD ANIMAL 



The vascular system as a whole is not filled to distension. 

 There is in the dead animal no uniform positive mean pressure 

 throughout the vascular system. If there did exist in the system 

 such a positive " mean hydrostatic pressure " when the heart is 

 arrested and the skeletal muscles are relaxed by death, it must be 

 produced by some secretory power of the vascular epithelium or 

 by the osmotic pressure of the blood. The blood must possess a 

 greater power of holding water than the tissues, and the wet film 

 of the capillary wall must be able to retain the water, so that the 

 whole system is filled to distension. The shrinkage of the face 

 in fainting, and how much more in death, shows the error of this 

 conception. After death there is a residual pressure in the aorta 

 owing to the resistance in the arterioles which contract and do 

 not allow the last of the blood to leak through into the capillary- 

 venous system. There is also a residual pressure in the venae cavae 

 produced by the influence of gravity and the post-mortem con- 

 traction of the viscera which drives the blood from the capillary 

 areas into the venae cavee. These residual pressures are, however, 

 unequal, and cannot be taken as representing a " mean hydrostatic 

 pressure " of the whole system. Thus the writer found in a 

 morphinised dog : 



