a. Hyperaemia is the result of active congestion, arising from idiopathic, sympathetic, or metastatic irritation, or it presents itself in the passive form as the precursor of asthenic inflammation, in consequence of a paralyzed state of organic innervation; or it may be purely mechanical, arising from obstruction to the circulation by pressure, incarceration of the intestine and its mesentery, contraction of the large vessels and the heart, impermeability of the lungs, etc, in which case it affects the veins chiefly. In consequence of the vascular injection, the mucous membrane of the intestine offers various degrees of redness, or there are slight extravasations or ecchymoses; or, as is particularly seen in the last two cases of hyperaemia, the mucous membrane, or even the entire membranes of the intestine, may present a uniform reddish-black color, the tissue being saturated with blood, and no injection of bloodvessels being distinguishable; the larger vessels, and particularly the venous trunks are distended even as far as the mesenteries, and overcharged with blood (apoplexia intestini). In either case hemorrhage may take place into the cavity of the intestine.

b. Anaemia of the intestinal mucous membrane occurs in connection with an atrophic state of the intestinal coats, and accompanying tabes universalis and general anaemia. It is often seen as a sequel of a rapid consumption of the vital fluids from excessive diarrhoea and exhausting discharges, and it appears in a very marked form in the gelatinous softening of the stomach and of the intestine in children. The intestine presents the color of tissue that has been rendered pale by maceration; or it may have the peculiar yellowish pallor of wax.