336 EDEMA 



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. c, liydrophil colloids, imbibe water with great avid- 

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

 varying under different conditions. The importance of tliis 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 swelling 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, and 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 affinity is mod- 

 ified by electrolytes, and change in a colloid may greatly alter its ca- 

 pacity for swelling; thus, ;8-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 colk)ids by enzymes. ^^ 



On the basis of the facts briefly summarized above, the proportion 

 of water present in any cell or in any fluid of the body which contains 

 colloids, is assumed to be determined by certain factors, namely (1) 

 the cliaracter of the colloids themselves; (2) the proportion and na- 

 ture of acids or alkalies present in the fluids in and about the colloids ; 

 (3) the proportion and nature of the salts. All these factors are 

 changeable, and tlierefore the amount of water present in the cell or 

 fluid varies accordingly. Thus, if a cell through its metabolism de- 

 velops from such a non-electrolyte as sugar (which has no consider- 

 able effect on the water content of the protoplasm), an organic acid, 



i3aAmer. Jour. Physiol., in07 (10), .-^eO: 1008 (22), 01. 



1* See Fischer's INlonopraph, "Oedema and Nepliritis."' New York. 1015; also 

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

 ou^'h discussion of this theory is contained in the biochemical l^villctin. Vol. T., 

 pivinj^ a bihliofijraphy 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 tlu^ swelling' of a tissue under the in- 

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

 degeneration (Wells, Jour. Exper. Med., 1000 (11), 1). 



