Diagnosis is necessarily incomplete, except we can ascertain with more or less confidence the cause upon which ascites depends. This is most apt to be overlooked when anasarca exists to such an extent, and its causes appear to be so definite, that the ascites is considered as only one manifestation of general dropsy. Un questionably its most common cause is obstruction of the portal circulation in disease of the liver, causing effusion of serum from the capillaries of the various venous branches which unite to form the vena porue. When this is produced by chronic inflam mation and shrinking of the liver, inflammatory thickening of the peritoneum often goes along with it, and probably aids the effect by interfering with absorption. It is also believed that chronic peritonitis may thus, without influencing the portal circulation, lead to accumulation of fluid, but acute peritonitis is never in the first instance associated with effusion. In the recognition of these two causes we are greatly aided by the history of the case ; the symptoms which more or less directly point to either condition will be reviewed in discussing the diseases of the liver and peri toneum. Occasionally no distinct indication is afforded, but the kidneys refuse to act, and the intestinal secretions, though goaded on by drastic purgatives, are insufficient to pump off the accumu lated fluid, until the abdomen is tapped, and then there is no fur ther difficulty in keeping the accumulation under control. In the
diagnosis of such cases we must not pretend to refine too much.
In a small number of cases occlusion of a vein produces ascites, just as it produces local oedema. Where the obstruction occurs before the intestinal veins reach the liver, the fluid will be limited to the peritoneum ; when it affects the inferior cava, anasarca of the lower limbs is also present. All of these are exceptional ; but when the cava is obstructed, evidence of an attempt at col lateral circulation over the surface of the abdomen will give a clue to the true explanation.
A genuine case of tympanites, when, from distension with gas, the abdomen is everywhere excessively resonant, cannot be mis taken for one of ascites ; but let us avoid the opposite error of overlooking the presence of fluid when much tympanitic disten sion exists. A very small amount of fluid, sinking low in the cavity of the abdomen, may readily escape observation, and yet it may be of much importance, as leading us to seek out the con current disease in the liver or peritoneum.