PATHOGENESIS OF EDEMA 347 



this protein will combine. Presumably the colloidal carbohydrates 

 and lipoids may also play a part in the water absorption of tisr^ues. 



Fischer's theory of edema, in his own words, is this: "A state of 

 edema is induced whenever, in the presence of an adequate supply 

 of water, the affinity of the colloids of the tissues for water is increased 

 above that which we are pleased to call normal. The accumulation 

 of acids within the tissues brought about either through their abnor- 

 mal production, or through the inadequate removal of such as some 

 consider normally produced in the tissues, is chiefly responsible for 

 this increase in the affinity of the colloids for water, though the possi- 

 bility of explaining at least some of the increased affinity for water 

 through the production or accumulation of substances which affect 

 the colloids in a way similar to acids, or through the conversion of 

 colloids which have but little affinity for water into such as have a 

 greater affinity, must also be borne in mind." In support of this 

 theory he advances evidence which he interprets as indicating that: 

 (i) "An abnormal production or accumulation of acids, or condi- 

 tions predisposing thereto, exist in all states in which we encounter 

 the development of an edema. (2) The development of an edema in 

 tissues is antagonized by the same substances which decrease the 

 affinity of the (h> drophilic) emulsion colloids for water (salts) and is 

 unaffected by uhe presence of substances which do not do this (non- 

 electrolytes). (3) Any chemical means by which we render possible 

 the abnormal production or accumulation of acids in the tissues is 

 accompanied by an edema." 



There are many features of lymph formation and edema with 

 which this theory seems to harmonize well, and others with which it 

 does not seem to agree so well, if at all, so that at this time it is a 

 fair statement that the theorj' is under consideration, but the limita- 

 tions of its applicability have not yet been agreed upon. It has met 

 with much adverse criticism, some of which was poorly founded, but 

 the fact cannot be disputed that the amount of water that colloids 

 will hold varies greatly with changes in the colloids. We may not 

 know absolute^, at present, whether the changes that take place in 

 the colloids during life are great enough to alter their water content 

 appreciably, but it is highly probable that they are. In many in- 

 stances the principles of colloidal hydration offer the best explanation 

 of observed conditions, and their application often elucidates matters 

 more satisfactorily^ than any other working hj'pothesis. Certainly 

 the}' cannot be disregarded in considering the factors that may come 

 into play in producing edema. 



Summary. — We find that a number of factors may be considered 

 as responsible for edema, some of them being prominent in one in- 

 stance, some in another, but in few cases can we consider one factor 

 alone as the sole cause. In most of the forms of edema, such as those 

 due to renal disease and cardiac disease, it now seems probable that 



