1906.] Obstruction of the Venw Cavce and the Portal Vein. 271 



the tissues. The urine is. diminished in amount, the animal refuses food, and 

 wastes. 



Obstruction above the Azygos Vein. 



Complete Occlusion. — I have been able to show that an animal may com- 

 pletely survive this operation. The animal lived for, three months, and at 

 the post-mortem examination the vein was absolutely occluded and not a trace 

 of oedema to be seen. The anastomoses were established by the comes nervi 

 phrenici, the internal mammary, and the azygos veins chiefly ; the veins of 

 the diaphragm were also distended. 



Before these anastomoses are established, however, oedema is regularly 

 produced, and apparently may directly lead to the deatli of the animal, or 

 absolutely disappear as in the above case. This can be proved by killing the 

 animal on the day after the operation or at a later date. (Edema of the 

 mediastinum, slight hydropericardium, and bilateral hydrothorax are found. 

 It seems to be the exception for all the fluid to be absorbed. One animal 

 died 18 days after the operation in an attack of dyspnoea, and 145 c.c. slightly 

 blood-stained fluid was found in the right pleural cavity and 125 c.c. in the 

 left ; oedema of the mediastinum was also present. I have never found any 

 free fluid in the peritoneal cavity. The urine is diminished in amount. 



Incomplete Occlusion. Diameter of Tube, 1 J mm. — The result of constriction 

 to this size is absolutely the same as that of complete ligature. As a fact, 

 the tube practically obliterates the vein, since water cannot be made to flow 

 through it post mortem. At any rate, if not absolutely obliterated, thrombosis 

 no doubt completes the obstruction. 



Diameter of Tube, 2 mm. (Edema of the mediastinum and hydrothorax 

 are produced in this case also. Eluid flows slowly through the constriction 

 post mortem. 



Diameter of Tube, 3 mm. — (Edema of the mediastinum is produced with 

 this constriction also, but only the merest trace of fluid in the pleural cavity 

 is found. Fluid flows quite easily through the constriction post mortem. 



Diameter of Tube, 4 mm. No oedema is produced by this amount of con- 

 striction of the superior vena cava. There is slight hsemorrhage and oedema 

 in the subcutaneous tissues at the seat of the wound, but this, as in all the 

 other cases, is the direct result of the injury to the tissues. 



The wall of the vein is so very thin that its diameter is practically 

 the same as that of the enclosing tube in the case of 3- and 4-mm. 

 constrictions. The general statement may therefore be made that when the 

 diameter of the superior vena cava is constricted to three-fifths of its normal 

 size, oedema of the mediastinum and hydrothorax begin to appear, and that 



