In pathological conditions percussion from above downwards may produce a tympanitic sound, due to gaseous indigestion or a clear sound throughout the greater portion of the vertical diameter suggestive of acute gastro-enteritis with the formation of gas in the rumen, or of adhesive peritonitis preventing the rumen from collapsing. Indigestion due to excess of solid food, on the contrary, is characterised by a dull sound throughout the entire region from above downwards. Percussion along a horizontal line permits of the delimitation of certain zones which vary a great deal in area, according to the case.
Auscultation is more instructive than percussion. Like percussion, it may be practised throughout the entire depth of the abdomen, from the transverse processes of the lumbar vertebræ as far as the white line, and in a horizontal direction from the eleventh rib to the region of the flank.
Auscultation of the upper zone enables one to detect sounds of deglutition, gurgling sounds (glou-glou), and a sound resembling falling water, due to the movement of solids or liquids in the rumen and reticulum. The sounds heard vary in different cases, and depend on the state of repletion or of emptiness of the rumen.
Auscultation of the middle zone reveals:
Firstly, a very special crepitation sound, which may be compared to the deflagration of a handful of salt thrown on burning coal. It is believed to result from the bursting of bubbles in the contents of the rumen under the action of normal digestion.
Secondly, a churning sound produced by the rhythmic peristaltic contractions of the rumen, by which the substances ingested are very intimately mixed. By applying the ear over the flank region or by palpation the rhythmic contractions of the rumen, two per minute in most cases, can readily be perceived.
In practice examination of the rumen is confined to these four methods.
Puncture. From an exclusively scientific point of view, exploration of the rumen also comprises analysis of the gas collected through puncture and analysis of the liquids removed by aspiration (first stages of gastric digestion). Normally, these gases, in the order of their abundance in the mixture, consist of the following: Carbonic acid, carburetted hydrogen and nitrogen.
In disease, and in most cases of abnormal fermentation, the carburetted hydrogen is greatly in excess of the carbonic acid. In chronic gastro-enteritis, ammonium sulphide and other offensive gases are found in addition.
Chemical analysis. In the rumen the ingested food is macerated in an alkaline liquid at a temperature of 100° to 101° Fahr. (the alkalinity is due to the saliva). This process markedly modifies the composition of the ingested matter. Nevertheless, the upper portion in contact with the gas sometimes presents a slightly acid reaction, probably due to carbonic acid. The sugary and fatty materials contained in the food respectively undergo lactic and butyric fermentation. Only a small quantity of the starch, however, is transferred into sugar. In the calf, and in very young animals, the reaction of the rumen is acid throughout the entire period of sucking. In disease, when rumination has long been suspended and chronic loss of appetite or gastro-enteritis exists, the reaction is generally acid. The sugars, gums, and soluble salts of forage, roots, etc., are dissolved in the rumen, but fatty materials undergo no modification.