In cases of very grave tympanites the gaseous pressure in the interior of the rumen appears to stop the crepitation sound. The animals soon become unable to walk or even to move, suddenly fall to the ground, and die rapidly from asphyxia.
The rapidity with which gaseous indigestion develops varies greatly. Sheep and oxen may die from tympanites, within an hour or even half an hour of their arrival in the field; but more frequently the symptoms develop slowly, only becoming alarming after some hours and continuing for twelve or even twenty-four hours without causing death.
As a rule, the gas is voided by a series of eructations which empty the rumen, and recovery follows; but when distension is extreme eructation cannot occur, and gaseous indigestion then ends in asphyxia and death.
Lesions. It might be imagined that this form of indigestion would only appear when the rumen contains a large quantity of food; but, in point of fact, the rumen often contains very little.
On post-mortem examination the rumen is found to contain an enormous quantity of gas, which, when collected and submitted to analysis, reveals approximately the following composition:—Carbonic acid, 74 per cent.; carburetted hydrogen, 24 per cent.; sulphuretted hydrogen, 2 per cent.; nitrogen, traces. The composition of this mixture varies within certain limits, according to its origin; but carbonic acid always predominates.
Lungwitz, after elaborate experiments with different foods kept in closed vessels at the body temperature and with similar agents fed for days as an exclusive aliment to oxen provided with a fistula of the rumen for purposes of collection, found carbonic dioxide the predominating gas in all cases, though the proportion varied with the nature of the food.
Marsh gas varied from 16 to 39 per cent., being especially abundant in cases of abstinence. Hydrogen sulphide was found only in traces. Oxygen and nitrogen were present in small amount, and were attributed to air swallowed with the food. In fermentation the oxygen may be completely consumed.
The abdominal organs, particularly the intestine, are congested, as a result of impediment to the venous circulation. The thoracic organs exhibit the lesions of asphyxia.
Pathogeny. Death is due to carbonic acid poisoning, brought about in two different ways—viz., progressive asphyxia, caused by inability to inflate the lungs, and absorption of carbonic acid gas from the rumen; by virtue of the laws of diffusion, part of the gas contained in the rumen passes into the blood.
The diagnosis is always very easy, and even farm servants may recognise the condition.