f)08 OEDEMA. [BOOK n. 



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 laby- 

 rinthine 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 physiological 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 accumulation of lymph in the latter. 



One kind of ojdcma we have already touched upon in speaking 

 of the capillary circulation (183), viz. the "inflammatory" oedema. 

 In this kind of oedema owing to changes in the vascular walls a 

 larger amount of transudation parses 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 o-dema. 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 arising 

 from obstruction to the venous flow: under these circumstances 

 more lymph passes into the lymph-spaces than the lymph-vessels 

 are able to carry away. If the femoral vein be tied the leg may 

 become oedematous, 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 accompaniment 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 obstruction the rise of pressure 

 within the small blood vessels is distinguished from that due to 

 arterial dilation by being accompanied with a want of adequate 

 renewal of the blood ; this probably affects the epithelioid lining 

 of the blood vessels in such a way as to increase the transu- 

 dation. And indeed, as is seen in cases of heart disease with 

 prolonged or repeated venous obstruction, the oedema as time 

 goes on and the tissues become impaired is more easily excited 

 and with greater difficulty removed, though the actual amount 

 of obstruction, the actual increase of pressure in the small vessels, 

 remains the same, or at least is not proportionally increased. 



