DROPSY In the discussion of the features of inflam mation, continual reference has been made to the cells that escape from the blood-vessels of the inflamed region and to the fluid which exudes from the over-full vessels. To these cir cumstances, it has been pointed out, is due in large measure the swelling that occurs in an inflamed area. It has also been pointed out that when the inflammation affects the mem brane lining any of the closed cavities of the body, a joint cavity, for instance, the pleural cavity, and so on, the exuded fluid may be in large quantity and may accumulate, distending the cavity, in which case it may be called a dropsical effusion.
In such cases the excessive effusion is due to the active determination of blood to the part because of inflammation.
But there are numerous cases where effusion takes place from the blood-vessels, which are over-full, not because of an active determination of blood to the part, but because of some ob struction to the onward flow. The blood comes to the part in ordinary quantity, but does not get away, because of some block to the onward flow.
This, therefore, seems a suitable place to explain all the circumstances in which dropsical effusions may occur.
Dropsy is an accumulation of fluid which has oozed out from the blood-vessels in the minute spaces in the tissue, or in some of the cavities of the body, the cavity of the belly for example.
It is called by a variety of names, according to the position of the accumulated fluid.
Dropsy confined to the tissue under the skin, in the foot, leg, or arm, for example, is called oedema or anasarca.
Dropsy of the belly is ascites (p. 266). The accumulation of fluid round the lung in pleurisy, to which the phrase pleural effusion is applied, (p. 359), is a dropsy, and a similar collection round the heart is called hydropericardium or dropsy of the heart (p. 318).
On p. 278 it is explained that fluid is con stantly oozing from the finest blood-vessels into the tissues to nourish them, that more fluid oozes than is necessary, and that the excess is picked up mainly by lymphatic vessels, and afterwards returned to the blood. Now, sup
pose more fluid escapes than can be picked up by the lymphatics, or suppose the absorbing vessels are somehow prevented fulfilling their purpose, the excess of fluid will remain and accumulate in the tissues, and in a short time that part will be the seat of dropsy.
Causes of dropsy are thus readily under stood. The quality of the blood may be so altered that fluid passes out very readily and in great excess. This happens in anaemia (p. 313), and in Bright's disease of the kidney (p. 399). Again, where obstruction exists to the return of blood to the heart, the blood accumu lates in the veins ; there is greater pressure on the blood, causing more to pass out of the vessels, and preventing also its absorption, and so dropsy again results.
This obstruction may be merely local. A tumour pressing upon the main vein of a limb will thus produce dropsy limited to that limb. In pregnant women the pressure of the en larging womb on the veins frequently causes swelling of the legs.
Dropsy may be more general. Thus in cer tain diseases of the liver the circulation is ob structed, and since all the blood from the belly and the lower limbs passes through the liver the obstruction is experienced in all these parts, and dropsy of both legs and of the cavity of the belly will soon ensue.
A more general cause even than this, and more common, is heart disease, where the on ward movement of the blood is hindered by some valve affection (p. 320) causing accumula tion of blood in the veins of lungs, liver, and other parts, and occasioning extensive dropsy. In such cases the parts at the greatest distance from the heart, and in the lowest situations, will feel the pressure of blood most, and will show the evidence of dropsical swelling soonest and most markedly, for example the feet and legs.