Passive hyperemia of the stomach is of very frequent occurrence, being brought about not only in that large class of cases in which there is a general venous engorgement, but also in those in which a localized lesion in the liver obstructs the portal circulation. The mucous membrane is generally reddened in such cases, and there is usually some catarrh. There are usually also haemorrhagic erosions visible (see below).

Severe vomiting also leads to passive hyperaemia, apparently by the spasmodic contraction of the muscular coat obstructing the veins. Here also there may be considerable haemorrhage.

Haemorrhage occurs under a considerable variety of circumstances. Ulcers, whether simple or cancerous, frequently cause it. It may result, as just mentioned, from passive hyperemia, and it occurs much more rarely in scurvy, purpura, yellow fever, and typhus.

In the case of ulcers there may be large haemorrhages from the rupture of considerable vessels. In passive hyperemia there is rather a leakage from the superficial vessels of the mucous membrane, these being least supported, and the blood passes chiefly into the cavity of the stomach. At the same time there is some infiltration of the mucous membrane in its superficial layers, and these parts being injured by the blood may be digested by the gastric juice. In this way arise small flat superficial ulcers, the so-called Haemorrhagic erosions. These are generally present in considerable numbers, chiefly in the pyloric region. In the erosions there may be still some remains of blackened blood, and alongside them there are little areas of mucous membrane infiltrated with blood. In these cases also the mucous membrane often presents a general redness from the passive hyperemia, and may be thickened by catarrh.

The blood, in whatever way arising, is generally mixed with the contents of the stomach, and blackened by the gastric juice. If the haemorrhage be very severe, as from an ulcer perforating a considerable artery, the blood may be vomited nearly in the fresh state, but usually it is tarry or like coffee-grounds. The altered blood will also pass into the duodenum and onwards.

Blood sometimes accumulates in the stomach when it has a different source, as when an aneurysm ruptures into the pharynx or oesophagus.