162 THE VASCULAR SYSTEM 



The mechanical theory as to the causation of cardiac dropsy 

 has been summed up by Bainbridge as follows : 



" First, in an uncompensated heart, there is a fall of arterial 

 pressure, and a rise of venous pressures near the heart. There is 

 also a fall of capillary pressure, in consequence of the fall of arterial 

 pressure, in the kidneys, intestines, and peripheral parts of the 

 body. The fall of capillary pressure lessens filtration, and for a 

 time upsets the balance between filtration and absorption ; con- 

 sequently an excess of fluid is absorbed by the blood vessels from 

 the intestines and peripheral tissues. 



" Secondly, this continued absorption associated with the 

 diminished urinary secretion, leads to hydraemic plethora, and 

 increases the mean systemic pressure. 



" Thirdly, this hydrsemic plethora raises the capillary pressure 

 all over the body, and promotes increased filtration, the more so 

 because the venous state of the blood damages the capillaries, 

 and increases their permeability. A further subsidiary factor is 

 the obstruction to the entrance of lymph into the great veins at 

 the thoracic duct owing to the excessive venous pressure." 



The writer controverts these views in each particular the 

 arterial pressure is not altered in uncompensated cases of heart 

 disease unless death is imminent ; neither is the venous pressure 

 altered, nor the capillary pressure. 



Neither hydraemic nor blood plethora raises the arterial venous 

 or capillary pressures excepting during the period of intra-venous 

 injection. Even if the capillary pressure were raised it would not 

 cause filtration because the blood in the capillaries and the tissue 

 lymph in any organ are and must be at one and the same hydro- 

 static pressure. 



THE EFFECT OF OBSTRUCTING THE BLOOD VESSELS 



While cessation of the blood flow in the " higher level " centres 

 of the brain abolishes consciousness in a second or two, perma- 

 nent recovery from a complete anaemia may occur which has lasted 

 some minutes, at the outside twenty minutes (Stewart and Guthrie). 1 

 The heart quickly stops beating when the coronary arteries are 

 closed, but can be recovered by transfusion hours after. Muscle 



1 A temporary recovery may occur after sixty minutes. Guthrie transplanted 

 the head of a dog, and obtained reflex movements of the eyes, &c. The circulation 

 in the hrain had been interrupted twenty-nine minutes. 



