344 EDEMA 



point more and more to the importance of vascular chang:es in acute 

 nephritis, at least.-" 



5. Increased Filterability of the Blood Plasma. — This takes 

 us back to Richard Bright 's conception of renal dropsy. He im- 

 agined that through the great loss of albumin in the urine the blood 

 became so thinned and watery that it could filter through the vessel- 

 walls, while normal plasma, he thought, was too thick and viscid to do 

 so. The same idea was applied to the edemas of cachexia in cancer, 

 etc., chlorosis, and all forms of edema associated with a decrease in 

 the corpuscular or protein elements of the blood. With our present 

 knowledge of diffusion of crystalloids and colloids we can readily ap- 

 preciate that a decrease in the blood colloids, such as might occur in 

 these diseases, could not modify the passage of fluids through the 

 capillary walls to any considerable degree. Stewart and Bartels con- 

 sidered that in renal dropsy the increased filterability of the plasma 

 was not due so much to the loss in albumin as to retention of water, 

 which caused an hydremic plethora. But this factor was soon elimi- 

 nated, for it was found that complete anuria, produced by ligating 

 both ureters, does not cause edema ; and also that to produce an edema 

 by increasing the water of the blood it was necessary to increase it 

 many times as much as it can ever be increased by disease. Simpl}^ 

 increasing the proportion of water by removing part of the blood and 

 injecting a corresponding amount of salt solution did not cause edema 

 iCohnheim and Lichtheim). We may, therefore, look upon the hy- 

 pothesis of increased filterability of the blood as chiefly of historic 

 interest, and not an important factor in the causation of edema. In 

 the presence of other factors for the production of edema, however, the 

 amount of fluid in the vessels is important; thus Pearce -' found that 

 in experimental uranium nephritis hydremia exerted a marked in- 

 fluence on the production of edema. 



6. Disparity of Osmotic Pressure in Favor of the Tissues and 

 Lymph over the Blood. — On a preceding page we have already 

 considered the means by which changes in osmotic pressure in the tis- 

 sues are brought about, and how they may lead to an accumulation 

 of fluid. The importance of osmotic pressure in causing pathological 

 edema was suggested by J. Loeb -^ in his studies on the physiological 

 action of ions. He stated that edema occurred when the osmotic 

 pressure was higher in the tissues than it was in the blood and lympli, 

 and the cause was to be sought in conditions that lowered the osmotic 

 pressure of the blood and lympli or raised that of the tissues. This 

 condition he found in the accumulation of metabolic products : — in 

 the case of muscle, totanization of a fi-og's muscle for ten minutes 

 raised the osmotic pressure over one atmosphere ; separating a muscle 



26 See Schmid and Sdilavcr, Dent. Arch. klin. Med., 1011 (104). 44. 



27 Arch. Int. Med., 1908 "(3), 422. 

 28Pfluger's Arch., 1898 (71), 457. 



