The local oedema seen in some nervous affections might be explained on the hypothesis of increased metabolic activity in these areas due to some local nervous stimulation.
It is probable that the kidneys also have an internal secretion, and that the great oedema sometimes found in kidney disease is rather due to the action of some proteid body resembling in its effects the streptococcus anti-toxin, than to accumulation of water due to imperfect action of the kidney.
They are enlarged to the size of an almond, rounded, firm and pink; there is some engorgement and oedema on section; the substance is rather soft, and can be scraped off with a knife.
Bainbridge suggests that a retention of metabolic products may cause the oedema in renal disease, Bradford having previously shown that loss of a certain amount of renal tissue caused retention of metabolic products in the tissues.
We find at this early stage oedema of the part.
Welch produced oedema of the lungs experimentally by increasing the pressure in the pulmonary vessels by ligature of the aorta and its branches, but this raised the blood pressure only about one-tenth of an atmosphere, while in some of Loeb's experiments the osmotic pressure, due to retained metabolic products, was equal to over thirty atmospheres.
There is general engorgement and oedema of the lungs, with pneumonic patches varying in size and irregularly distributed.
The physical signs are those of broncho-pneumonia; oedema of the lungs soon supervenes, and death occurs in three or four days.
Thus differences in osmotic pressure may be much more powerful in producing oedema than mere differences in blood pressure.
It is invariably the result of some cause acting generally, such as renal disease, valvular defect of the heart, or an impoverished state of the blood; while a mere oedema is usually dependent upon some local obstruction to the return of blood or lymph, or of both, the presence of parasites within the tissue, such as the filaria sanguinis hominis or trichina spiralis, or the poisonous bites of insects.