188 FRANKLIN C. McLEAN 



weight, without producing edema. When, however, the capillaries were 

 injured by poisons such ejections caused marked edema, even though the 

 kidneys remained active. Cohnheim concluded that salt and water were 

 retained by the tissues because the blood vessels could no longer hold them, 

 and not on account of insufficiency of the kidneys. 



Ambard and Beaujard demonstrated the occurrence of chlorid reten- 

 tion without edema in cases of interstitial nephritis. Brasch has found 

 the sodium chlorid content of the blood as high as 10 grams per liter in 

 cases of anuria, without edema. 



Whether the actual cause of retention of sodium chlorid and water 

 in the body depends on insufficiency of the kidneys, or on alterations in 

 the permeability of the capillary walls, or in the cell metabolism, the 

 mechanism of the relation of salt and water intake to edema may be 

 conceived as follows: 



The blood, under normal conditions, and even under abnormal circum- 

 stances, tends, by some regulating mechanism, to maintain its volume, its 

 concentration of electrolytes, and its osmotic pressure at remarkably con- 

 stant levels. The forces concerned in this mechanism are those just dis- 

 cussed, but regulation of the mechanism is not understood. Under normal 

 circumstances, any excess of salts or of fluid is rapidly excreted through 

 the kidneys, though these substances may be temporarily stored in the 

 tissues. Under abnormal conditions, such as obtain in heart failure and in 

 nephritis, fluid and salt remain in the tissues to form edema. If, as a 

 result of excretion and diminished intake, the chlorid and water content 

 of the plasma tend to fall below normal, these substances are withdrawn 

 from the tissues, the volume of fluid in the tissues is diminished and edema 

 tends to disappear. The process is analogous to the behavior of these sub- 

 stances in the normal organism, except that the organism as a whole is 

 not able to dispose of the usual excess of fluid and salt ingested. As has 

 been shown, such fluids as remain in the tissues in edema are maintained 

 in appropriate osmotic equilibrium with the blood, so that salt and water 

 have a mutual attraction for each other, and both are necessary for the 

 occurrence and persistence of edema. 



PART V 



The Treatment of Edema 



Only those methods of treatment of edema are discussed which are 

 directed toward the regulation of metabolic processes. For other methods 

 of treatment, especially mechanical methods, treatises on general medicine 

 should be consulted. 



Prophylaxis. As edema is usually a secondary or symptomatic con- 

 dition, its prophylaxis depends on treatment of the primary condition, 



