Observations on Digestion in the Ruminant

PRESENT-DAY knowledge of the physiology of digestion in ruminants is very limited and to a great extent it is based on anatomical deductions. Some of these are doubtless correct; but many of them must be regarded merely as speculations until such time as adequate experimental proof is brought forward. It was with the object of providing this proof that the present work was undertaken. The experiments were concerned chiefly with the progress of the food through the alimentary canal, and, consequently, with the movements of the different sections of the canal itself. The ruminant owes its unique position amongst mammals to the anatomical complexity of the stomachs, and, for this reason, attention was directed particularly to the movements of these viscera. It will be an advantage, before taking up the experimental part of this paper, to consider certain important anatomical features and postmortem appearances and to discuss the physiological significance which it is believed can be attributed to them. The ruminant possesses four so-called stomachs—the first or reticulum, the second or rumen, the third or omasum and the fourth or abomasum. Only the abomasum has the characteristics of a stomach, because it alone secretes a digestive fluid, whereas the lining epithelium of the other three viscera is devoid of secreting cells of any kind. Furthermore, the first three pouches arise from the caudal end of the wall of the oesophagus. These pouches are rudimentary at birth and during suckling life; but they develop rapidly after the animal begins to eat coarse fodder. Neither on anatomical nor physiological grounds, therefore, can the first three viscera be classified as stomachs. The term "fore-stomachs" ("Vormagen" of German workers) is more appropriate. They are not secreting organs, and the only digestive juice present normally in them is saliva; this has been shown to contain no ptyalin (Trautmann and Albrecht, 1931), so that the only chemical changes which can occur in the fore-stomachs are those due to fermentation. The contents of the reticulum and rumen are always fluid, and there is no doubt that the organs represent chambers where mixing and fermentation occur. The two pouches communicate freely with each other, and the term " reticulo-rumen " can be correctly applied to