DILATATION, a widening or enlarging; a term used in physiology, etc. In pathology the process is of great importance as it may be compatible with health or the cause of changes so severe that they menace life. In the case of blood vessels dilata tion of arteries occurs in blushing and in every inflammation at some stage in its course; dilatation of the abdominal blood vessels is the cause of syncope and shock in many instances and dilata tion of veins accompanies every case of passive congestion. In the case of lymphatics dilatation is the cause of elephantiasis. In the case of hollow organs like the heart, bladder, stomach or intestines dilatation, if great and of rapid onset is accompanied by severe pain (e.g. angina pectoris) and if continued is fol lowed by temporary paralysis of the organ's musculature. In the case of the brain, dilatation of the lateral ventricles causes hydro cephalus (q.v.) dilatation of the central canal of the spinal cord causes the special symptoms depending on syringomyelia. If the dilatation of hollow muscular organs is gradual there may be time for hypertrophy to occur and compensate for the dilata tion. This is typically the case with the left ventricle of the heart in cardiac disease but ultimately dilatation gains the upper hand and initiates the terminal stages of the illness. (W. S. L.—B.)