336 EDEMA 



osmotic pressure in lymph formation. ^^ For example, the lymph 

 contains more chlorides and may have a much higher osmotic 

 pressure than the serum of the same animal (Hamburger, Carlson, 

 et al.).'' 



Variable Capacity of Colloids for Water. — Colloids of the type of the 

 tissue proteins, i. e., hydrophil colloids, imbibe water with great avid- 

 ity, until a certain proportion of water is present, the proportion 

 varying under different conditions. The importance of this force in 

 the production of edema and related processes was first pointed out 

 by Martin H. Fischer, and has been developed extensively by him." 

 The amount of water which a given hydrophil colloid, such, for exam- 

 ple, as gelatin, or fibrin, will take up, is greatly modified by the reac- 

 tion of the solution and by its content of electrolytes. Very small 

 concentrations of acids or alkalies will greatly increase the amount 

 of water absorbed, while salts reduce it, and the different acids and 

 salts vary in their effects; thus hydrochloric acid causes a greater 

 swelling of colloids than a corresponding strength of sulphuric acid, 

 and calcium chloride depresses the swelhng more than potassium 

 chloride. The effect of the salts is made up of their constituent ions. 

 Non-electrolytes have relatively little effect. The forces developed 

 by this affinity of colloids for water are enormous; thus, to prevent 

 the taking up of water by starch requires a pressure of over 2500 at- 

 mospheres, dried gelatin will take up 25 times its weight of water, 

 and fibrin as much as forty times. Different colloids differ greatly in 

 their affinity for water and in the way in which this afl&nity is modi- 

 fied by electrolytes, and change in a colloid may greatly alter its 

 capacity for swelling; thus, jS-gelatin, which can be formed from ordi- 

 nary gelatin by the action of proteolytic enzymes, has greater capacity 

 for swelling than the original gelatin. Gies especially lays stress on 

 this factor, that is, the alterations of the hydrophilic tendencies of the 

 tissue colloids by enzymes.'^ In the plant world we find striking 

 examples of this character; thus, the succulence of some plants results 



15 Gunzberg (Arch. ncerlandphysioL, 1918 (2), 364) states that the passage of 

 water into the intercellular spaces is due to the electrical properties of the mem- 

 brane separating the circulating fluid from the tissues. The element potassium 

 and the ioas H and OH play an important part in this electrical osmosis which is 

 able to drive the fluid in the opposite direction to osmotic pressure. Thus, a 

 dialyzing sack containing Ringer solution minus K immersed in Ringer solution 

 loses weight. Perfusion of frogs with Ringer solution minus K produces marked 

 edema. 



16 Amer. Jour. Physiol., 1907 (19), 3G0; 1908 (22), 91. 



1' See Fischer's Monograph, "Oedema and Nephritis," New York, 1915; also 

 numerous articles in the Zeit. f. Chem. u. Ind. d. Kolloide. An especially thor- 

 ough discussion of this theory is contained in the Biochemical Bulletin, Vol. I., 

 giving a bibliography of Fischer's work, together with articles on Gies' observa- 

 tions on the modification of the hydrophilic tendency of proteins by enzyme 

 action. 



1* A definite and clear-cut example of the swelling of a tissue under the in- 

 fluence of acid of metabolic origin is shown in the muscle cell in Zenker's waxy 

 degeneration (Wells, Jour. Exper. Med., 1909 (11), 1). 



