CEDE'MA (Gr. a swelling) is the term applied in medicine to the swelling occasioned by the effusion or infiltration of serum into cellular or areolar structures. The subcu taneous cellular tissue is the most common, but is not the only seat of this affection. It is occasionally observed iu the submucous and subserous cellular tissue, and in the cell ular tissue of the parenchymatous viscera; and in some of these cases, it gives rise to symptoms which admit of easy recognition during life. Thus oedema of the glottis (see LARYNX) and oedema of the lungs constitute well-marked and serious forms of disease; while oedema of the brain, though not easily recognized during life, is not uncommonly met with the examination of insane patients.
(Edema may be either passive or active, the former being by far the most common. Passive adorn', arises from impeded venous circulation (as from obstruction or obliteration of one or more veins; from varicose veins; from standing continuously for long periods, till the force of the circulation is partly overcome by the physical action of gravitation; from deficiency in the action of the adjacent muscles, which in health materially filth the venous circulation, etc.); from too weak action of the heart (as in dilatation or ce• tain forms of valvular disease of that organ); or from a too watery or otherwise diseased state of the blood (as in chlorosis, scurvy, Bright's. disease, etc.). By means of the
knowledge derived from pathological anatomy, we can often infer the cause from the scat of the swelling; for example, oedema of the face, usually commencing with the eye lids, is commonly caused by obstruction to the circulation through the left side the heart, or by the diseased state of the blood in Bright's disease; and °Aetna of the lower extremities most commonly arises from obstruction in the right side of the heart, unless it can be traced to the pressure of the gravid uterus, or of accumulated foetus in the colon, or to some other local cause.
Active cedema is associated with an inflammatory action of the cellular tissue, and is most marked in certain forms of erysipelas. It is firmer to the touch, and pressure with the finger produces less pitting than in the passive form.
From the preceding remarks, it will be seen that oedema is not a disease, but a symp tom, and ofen a symptom indicating great danger to life. The means of removing it must be directed to the morbid condition or cause of which it is the symptom.