278 Dr. C. Bolton. Dropsy produced by [Dec. 19,. 



The smallest constriction, therefore, of the inferior vena cava, which is; 

 necessary to produce any effect upon the blood-pressures, will give rise to. 

 ascites. 



4. Effects of Obstruction of the Portal Vein. 

 (a) Upon the Production of Dropsy. 



Complete Occlusion. — Ligature of the portal vein at the spot where it enters; 

 the liver brings about death in a variable number of hours. There is 

 regularly found about 6 or 10 c.c. slightly blood-stained fluid in the peritoneal 

 cavity and small haemorrhages in the mesentery may be seen. Since ligature 

 of the superior mesenteric vein causes hemorrhagic infarction of the intestine, 

 whilst ligature of the portal vein does not, the latter fact is to be explained 

 by the circumstance that the veins from the stomach and spleen are included 

 in the ligature, and, therefore, a certain amount of venous anastomosis can 

 become established and the spleen itself can act as a reservoir, but the 

 anastomoses are not sufficient to prevent the occurrence of dropsy or the- 

 great fall of arterial blood-pressure which brings about the death of the 

 animal. 



Incomplete Occlusion. Diameter of Tube, 1-J mm. — Constriction of the portal 

 vein down to 1J mm. diameter may or may not cause the death of the- 

 animal. 



If the animal dies, about the same amount of free ascitic fluid is found in 

 the peritoneal cavity as when the portal vein is completely ligatured. If the 

 animal lives and is killed on the following day, 20 c.c. fluid, free from blood, 

 may be found in the peritoneal cavity. 



This is precisely what would be expected, since the animal lives longer than 

 when the vein is completely occluded, the obstruction not being so great. 



Diameter of Tube, 3 mm. — Constriction to a diameter of 3 mm. likewise 

 produces ascites in small amount, about 10 c.c. perfectly clear fluid being 

 found in the peritoneum on the day after the operation. This fluid, however, 

 may be absorbed, because in an animal whose portal vein had been constricted 

 to this diameter seven weeks previously no ascites was found. The fluid may 

 also be absorbed when the portal vein is constricted to 2 mm. in diameter. 



Diameter of Tube, 4 mm. — In most large animals the diameter of the- 

 portal vein is just over 4 mm. in size, and a slight but definite constriction is 

 produced by a tube of 4 mm. in diameter. Ascites, however, is not produced 

 by such a procedure, the abdominal cavity being perfectly normal. 



Speaking broadly, therefore, constriction of the portal vein to about 

 three-fourths of its normal diameter will give rise to dropsy of the 



