DIGESTION 195 



As food arrives in the rumen it passes into what Colin has 

 described as the lower story, a part which never empties itself, 

 and consists of the usual coarse ingesta and fluid. As the 

 stomach fills, the mass extends into the upper story, the stomach 

 dilating, and finally the reservoir becomes full to the roof, 

 though not tightly packed. The last arrival in the rumen is 

 naturally received in the anterior extremity of the left sac, and 

 from here it passes through all hemispheres of the rumen. 

 Material from the posterior part of the rumen makes its way 

 forwards towards the oesophageal opening for remastication, 

 and there can be no doubt that the mass in these sacs is actually 

 revolved ; for material capable of identification, if introduced 

 into the stomach through a wound in the abdominal wall, gradu- 

 ally disappears, and returns to the same place in from twelve 

 to twenty-four hours. 



Colin, through the window in the abdominal wall, was able, 

 by illumination, to inspect the interior during digestion, and 

 while food was still arriving in the compartment. He observed 

 that the level of the mass varied from moment to moment, 

 rising and falling alternately ; he could even see a portion rise 

 up out of the mass, detach itself, and pass backwards. At other 

 times the detached portion moved forwards ; in either case it 

 disappeared into the body of the organ, and was churned up 

 again later on. During rumination or when fluids are swal- 

 lowed this oscillation of the mass is most energetic, and, as Colin 

 expresses it, the flow and return flow are most interesting to 

 witness. They induce the most complete mixing of the contents, 

 that which was at the top passing to the bottom, while the 

 material at the bottom passes to the top. Evidence of the 

 complete nature of the churning movements of the rumen is 

 afforded by the perfectly spherical ' hair balls ' which are some- 

 times found there. Stimulation of the mucous membrane of the 

 rumen provokes contraction of the walls, especially of the 

 muscular pillars. 



The contents of the rumen are alkaline generally, more markedly 

 in the lower than in the upper parts, where, in fact, a slightly 

 acid reaction may be obtained from food fermentation. Very 

 frequently the nature of the reaction is doubtful. The alkaline 

 reaction is due to the saliva, for there is no secretion from the 

 wall of the rumen. 



The essential function of the rumen is to retain the food fo r 

 remastication, to macerate all fibrous substances and to fit them 

 for cellulose digestion, which here takes place possibly under 

 the influence of ferments contained in the food itself. The 

 amount of cellulose digested in the rumen has been estimated 

 at between 60 and 70 per cent. The result of the decomposition 



