294 EDEMA 



also the urticarias which follow the ingestion of various toxic 

 substances, many of which can be shown experimentally to be 

 lymphagogues. A good example is the urticaria which often 

 follows the injection of antitoxic or other foreign serums, par- 

 ticularly their repeated injection ; in experimental animals such 

 a serum may cause death very quickly by acute pulmonary 

 edema. All these poisons probably produce urticarial edema 

 by injury to the capillary walls in the subcutaneous tissues 

 probably the other factors are not important in this condition. 

 In the action of vesicants, however, it may well be questioned 

 if changes in the capillary walls and active hyperemia are not 

 supplemented by local metabolic alterations and osmotic influ- 

 ences. 



Neuropathic Edema. Until we understand better than 

 we now do the manner in which nervous impulses modify metab- 

 olism, it will be difficult to estimate properly the importance 

 of nervous impulses in the production of edema. That nervous 

 control is a possible factor is well shown by many experi- 

 ments ; for example, simple ligation of the femoral vein in 

 animals does not cause edema, but if the sciatic nerve is cut 

 the vasoconstrictors are paralyzed, and edema may follow 

 (Ranvier). In this case the nervous influence is only indirect, 

 through its vasomotor effects. Similarly, stimulation of vaso- 

 dilator fibers may cause edema. It is furthermore possible that 

 nervous stimulation may lead to excessive metabolic activity, 

 with an accumulation of crystalloidal products, sufficient to 

 cause edema when supplemented by active congestion and some 

 resulting pressure upon the lymph-vessels. There are certainly 

 many instances in which edema seems to depend upon nervous 

 disturbance ; for example, edema in the area of distribution of 

 a neuralgic nerve ; sudden joint effusions in tabetic arthropathy ; 

 and especially the typical " angioneurotic " edema. The only 

 explanation that seems open is the one given above, namely, a 

 combination of local hyperemia and increased metabolic activity. 



Hereditary Edema. In a number of families there has been 

 observed a peculiar inherited tendency to the occurrence of acute 

 attacks of local edema, which not infrequently have proved fatal 

 when involving the glottis. 1 There can be little question that 

 these instances of hereditary edema depend upon a nervous 

 affection of some kind, it being practically an angioneurotic 

 edema; but how the edema is produced, and what the nature 

 of the nervous alteration may be, are as mysterious as are most 

 other so-called " nervous inheritances." 



1 Literature, see Fairbanks, Amer. Jour. Med. Sci., 1904 (127), 877. 



