582 PRACTICE OF PHYSIC. 



the body to the right ventricle of the heart. This interruption 

 seems to operate by resisting the free passage of the blood from 

 the arteries into the veins, thereby increasing the force of the ar- 

 terial fluids in the exhalents, and consequently the quantity of 

 fluid which they pour out. 



MDCXLIX. The interruption of the free return of the 

 venous blood from the extreme vessels, may be owing to certain 

 circumstances affecting the course of the venous blood ; very 

 frequently to certain conditions in the right ventricle of the 

 heart itself, preventing it from receiving the usual quantity of 

 blood from the vena cava ; or to obstructions in the vessels of 

 the lungs preventing the entire evacuation of the right ventricle, 

 and thereby hindering its receiving the usual quantity of blood 

 from the cava. Thus, a polypus in the right ventricle of the 

 heart, and the ossification of its valves, as well as all consider- 

 able and permanent obstructions of the lungs, have been found 

 to be causes of dropsy. 



MDCL. It may serve as an illustration of the operation of 

 these general causes, to remark, that the return of the venous 

 blood is in some measure resisted when the posture of the body 

 is such as gives occasion to the gravity of the blood to oppose 

 the motion of it in the veins, which takes effect when the force 

 of the circulation is weak ; and from whence it is, that an up- 

 right posture of the body produces or increases serous swellings 

 in the lower extremities. 



MDLI. Not only those causes interrupting the motion of the 

 venous blood more generally, but farther, the interruption of it 

 in particular veins, may likewise have the effect of increasing 

 exhalation, and producing dropsy. The most remarkable in- 

 stance of this is, when considerable obstructions of the liver 

 prevent the blood from flowing freely into it from the vena por- 

 tarum and its numerous branches ; and hence these obstructions 

 are a frequent cause of dropsy. 



MDLII. Scirrhosities of the spleen and other viscera, as 

 well as the scirrhosity of the liver, have been considered as 

 causes of dropsy ; but the manner in which they can produce 

 the disease I do not perceive, except it may be where they 

 happen to be near some considerable vein, by the compression 

 of which they may occasion some degree of ascites ; or, by com- 



