Passive Hypermnia. 115 



with low arterial pressure, the blood not being properly propelled 

 through the capillaries, in connection with deficiency in the pro- 

 pelling power of the heart and arteries or complete loss of the 

 arterial reactions (atonic hypcmmia). When the blood is not kept 

 moving onward, in compliance with the law of gravitation it set- 

 tles into the dependent parts of the body. As the animal lies on 

 one side the lowest parts become the seat of special engorgement 

 (one half the lungs in the cadaver). This hypostatic or gravita- 

 tion hypercsmia (hypostasis) takes place because of the longer 

 persistence of the blood in fluid condition in the capillaries as 

 compared with the larger vessels. It may be noted in animals 

 unable to raise themselves from the ground in long protracted 

 diseases or in the agonal period, and may also develop after 

 death. It may, however, develop in a nondependent organ because 

 of reduction in its arterial supply, particularly if the blood pressure 

 in the venous trunk be so great that the blood presses back from 

 the veins into the capillaries no longer filled from the arterial 

 side. Since the progression of the blood in the veins depends 

 in part upon general muscular movements and the passage of 

 blood from the venae cavse is particularly favored by the inspira- 

 torv expansion of the thorax, deficiency in body movements and 

 in respiratory activity (pulmonary diseases), as may be expected, 

 promote the development of hypostatic congestion. The most 

 common obstacle to the venous circulation arises from compression 

 of the delicate walls of the veins by external pressure, kinking as 

 in intestinal volvulus, constriction or pressure from tumors; reduc- 

 tion of the venous lumen or actual obstruction from thrombosis 

 should also be mentioned in the same connection. 



Passive congestion of the portal vein and its branches, afifecting 

 the spleen, stomach and intestines [and pancreas] is occa- 

 sioned by all diseases of the liver accompanied by shrinkage or 

 reduction of the capillary network of the organ, the condition 

 interfering with the progression of the portal blood through the 

 liver. 



Widespread passive hyperaemia is met in case of cardiac valvu- 

 lar lesions because of the interferences oflr'ered to the ready move- 

 ment of the blood from the venge cavse and pulmonary veins. 



A passive congestion caused by local interferences may have no 

 further results provided the venous trunk in question or its tributary 

 capillaries communicate by collateral circulation with other veins 

 which are not affected, the blood then passing freel}- through such 



