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



it is possible, but not usual, for an animal to absorb the fluid and completely 

 recover when the superior vena cava is absolutely obliterated. This state- 

 ment applies to constrictions which are suddenly produced. 



(b) Upon the Circulation of the Blood. 

 Arterial Pressure. 



Complete ligature of the superior vena cava produces only a very slight 

 effect upon the arterial blood-pressure curve. The output of the heart 

 is slightly diminished, and there may be a very trifling fall in the pressure, 

 but usually there is none. On the following day, when the animal has 

 developed dropsy, the blood-pressure is of precisely the same height as it was in 

 the normal animal. The fact that there is no immediate fall in the blood- 

 pressure on complete ligature of the superior vena cava was, of course, well 

 known in the days of Cohnheim (3). 



Constriction of the superior vena cava similarly brings about no alteration 

 in the height of the blood-pressure tracing. 



Venous Pressure. 



External Jugular Vein. — A gradually increasing constriction of the superior 

 vena cava produces no change whatever upon the pressure at the upper end 

 of the external jugular vein, until the former vein is narrowed to a diameter 

 of 3 or 2 J mm. At this point the pressure in the jugular vein rises to a 

 height varying from 20 to 40 mm. MgS0 4 solution above what it was before 

 the constriction was commenced. 



Complete ligature causes a rise of pressure at the upper end of the external 

 jugular vein of about 130 mm. MgS0 4 solution above the normal. This 

 high pressure is not maintained, for, whether the superior vena cava has been 

 completely ligatured or merely constricted, the pressure in the jugular vein 

 gradually falls, and within the space of about an hour has reached the normal 

 limit once more. On the following day, when the animal has developed dropsy, 

 the venous pressure in the external jugular vein is still normal. 



The following experiment shows the effects of obstruction of the superior 

 vena cava upon the pressure at the upper end of the external jugular 

 vein : — 



