It is generally conceded that in several types of edema there is some disturbance in the inorganic ion balance of the body. This is particularly true of edema associated with various forms of renal disease. Whether this imbalance as evidenced by retention of salts, particularly sodium chloride, within the tissues, plays a primary or a secondary rôle is a subject much disputed. The difficulty, if not impossibility, of reproducing edema experimentally has delayed the solution of this problem.
Experimental studies indicate that, apart from the comparatively simple form due to lymphatic obstruction, the production of edema is dependent on several factors, the individual importance of which varies in different instances. The chief of these may be enumerated as follows: (1) increased capillary permeability; (2) alterations in osmotic pressure, and (3) increased affinity of tissue colloids for water. The exact relation of the retention of salt to these phenomena and to