THE NATURE AND MOVEMENTS OF LYMPH. 323 



qtient 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 physiological changes in the walls of the lym- 

 phatic 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 cedema we have already touched upon in speaking of the 

 capillary circulation ( 169), viz., the "inflammatory" 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 cedema is 

 the increase of lymph, also apparently changed somewhat in character, 

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

 as iu pleurisy and peritonitis. 



One of the most common forms of oedema is an cedema 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 cedematous, and, as we have said, cedema is 

 a common result of the plugging or obstruction of veins through disease ; 

 the cedema which is so common an accompaniment of heart disease, involv- 

 ing 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 cedema 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 bloodvessels is distinguished from that due to arterial dila- 

 tation by being accompanied with a want of adequate renewal of the blood ; 

 this probably affects the epithelioid lining of the bloodvessels in such a way 

 as to increase the transudation. And, indeed, as is seen in case of heart dis- 

 ease 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 

 proportionately increased. 



Still another kind of oedema is one due to changes taking place in the 

 blood, quite apart from variations of blood-pressurer This kind of oedema 

 is seen in some diseases of the kidney, in " Bright's disease," for instance. 

 In such cases the blood contains less proteids, and indeed less solids, is more 

 watery and of lower specific gravity than is normal. But the oedema is not 

 in these cases to be explained on the view that the more watery blood passes 

 more readily through the capillary walls, for it may be shown experimentally 

 that the mere thinning of the blood, as by the injection of normal saline 

 solution into the bloodvessels, will not at once lead to cedema, at least in the 

 limbs and trunk, and it is these which in Bright's disease especially become 

 cedematous. In all probability the oedema of Bright's disease, if it be really 

 due to the abnormal character of the blood, is produced by the abnormal 

 blood so acting on the bloodvessels that these allow a transudation greater 

 than the normal. Finally, oedema may be due to abnormal conditions of 

 the tissues themselves. 



