292 EDEMA 



channels, and perhaps also, in the case of cardiac incompetence, 

 obstruction to the discharge of lymph from the thoracic duct 

 into the subclavian vein against the high intravenous pressure. 



Renal Edema. We must recognize under this heading 

 two different types of edema. In acute nephritis (e. g., in 

 scarlatina) toxic materials appear to be the chief cause, and, as 

 Senator contends, injure alike the capillaries of the renal glom- 

 erules and of the subcutaneous tissues ; in each case there results 

 an increased permeability which is manifested by albumin uria 

 as a result of the injury to the renal capillaries, and by edema 

 as a result of the injury to the tissue capillaries. This sort of 

 edema is allied to that produced by peptone and similar lympha- 

 gogues, and we might well imagine that the mechanism con- 

 sisted merely in an injury to the capillaries through which 

 excessive fluid is driven by the blood pressure, were it not for 

 such observations as those of Mendel and Hooker, 1 who found 

 that postmortem flow is increased by these lymphagogues also. 

 We can hardly account for the force exhibited in postmortem 

 lymph flow on any other ground than that it is furnished by 

 osmotic pressure, unless we wish to fall back upon " vital activ- 

 ity" of the surviving cells. Hence it is probable that even in 

 the edemas of toxic conditions, such as acute nephritis, osmotic 

 pressure plays a part, the pressure-raising substances probably 

 being abnormal or excessive metabolic products of the cells 

 affected by the poisons. 



In the more common edema of chronic nephritis we have to 

 consider, among other factors, the blood pressure. That this is 

 not an essential or even important cause, however, is shown by 

 the fact that edema is usually much less marked in interstitial 

 nephritis with high blood pressure than it is in parenchymatous 

 nephritis with a much lower pressure. Toxic substances are, of 

 course, also present in the blood, and may alter capillary per- 

 meability ; these toxic substances may account for the localized 

 edemas and erythemas sometimes observed in nephritis. But 

 probably most important is the action of the crystalloids which the 

 kidney does not excrete, and which seem to be stored up in the 

 tissues, where they cause transudation of water under the influ- 

 ence of their osmotic pressure. For example, Rzentkowski 2 

 found that the average lowering of the freezing-point by the 

 edematous fluid in nephritis was 0.583, in cardiac dropsy it 

 was 0.548, and in tuberculous pleuritis 0.526. This indicates 

 that the osmotic concentration of the fluid is highest in renal 



1 Amer. Jour, of Physiol., 1902 (7), 380. 

 2 Berl. klin. Woch., 1904 (41), 227. 



