410 (EDEMA. [BOOK n. 



tion to the flow of lymph from the lymph-spaces, and on the 

 other hand an excessive transudation, the lymph gathering in 

 the lymph-spaces faster than it can be carried away by a nor- 

 mal flow; with the former the lymphatic system itself, with 

 the latter chiefly the vascular system is concerned. As a mat- 

 ter of fact, however, oedema is almost always, if not always, 

 due to abnormal conditions of the vascular system, and is the 

 result not of hindered outflow but of excessive transudation. 

 Owing to the numerous anastomoses of the lymph-vessels and 

 the consequent establishment of collateral streams, obstruction 

 in the lymph-passages themselves rarely if ever gives rise to 

 oedema ; and it may be here remarked that owing to the same 

 free collateral communication between the lymph-vessels the 

 labyrinthine passages of the lymphatic glands do not offer the 

 serious obstacle to the onward flow of the general lymph-stream 

 as might at first sight be supposed. Nor have we at present 

 any knowledge which would lead us to suppose that any physi- 

 ological changes in the walls of the lymphatic vessels or of the 

 lymph-capillaries, or in the lymph-spaces, by giving rise in some 

 way to obstacles to the flow of lymph, ever lead to an accumu- 

 lation of lymph in the latter. 



One kind of oedema we have already touched upon in speak- 

 ing of the capillary circulation ( 161), viz. the "inflamma- 

 tory" oedema. In this kind of oedema owing to changes in 

 the vascular walls a larger amount of transudation passes into 

 the lymph-spaces, and that transudation is richer in proteid 

 matters, and contains a larger amount of the fibrin factors, or 

 at all events is much more distinctly coagulable than ordinary 

 lymph, as well as crowded with migrating corpuscles. Allied 

 to this inflammatory oedema is the increase of lymph, also 

 apparently changed somewhat in character, which appears as 

 " effusion " in the serous cavities when these are inflamed, as 

 in pleurisy and peritonitis. 



One of the most common forms of oedema is an oedema of 

 primarily, though not wholly, mechanical origin, oedema aris- 

 ing from obstruction to the venous flow ; under these circum- 

 stances more lymph passes into the lymph-spaces than the 

 lymph-vessels are able to carry. If the femoral vein be tied 

 the leg may become cedematous, and, as we have said, oedema 

 is a common result of the plugging or obstruction of veins 

 through disease ; the oedema which is so common an accompa- 

 niment of heart disease involving obstruction to the return of 

 venous blood to the right side of the heart, and the ascites 

 which follows upon hindrance to the portal flow are instances 

 of oedema of this kind. We have already remarked on the 

 relation of transudation to blood-pressure ; and in venous ob- 

 struction the rise of pressure within the small blood vessels 

 is distinguished from that due to arterial dilation by being ac- 



