DIGESTION 207 



pared until its return must occupy 545 seconds. One minute 

 might be taken as sufficiently near. Rumination is, therefore, 

 a slow process, and occupies at least seven hours out of the 

 twenty-four. It is remarkable the length of time an animal 

 will continue to ruminate while using the jaws in one direction ; 

 from the effort involved frequent changes of direction might have 

 appeared to be necessary, but such is not the case. One- quarter 

 to half an hour's mastication on one side may be performed. 



The animal prefers a recumbent position for the process, 

 but draught oxen may be seen ruminating in the yoke, and camels 

 while carrying their burden. 



The share taken by the reticulum is mainly the supply of 

 fluid to the mass, but rumination can occur even after the 

 removal of the reticulum. A certain distension of the rumen 

 is absolutely necessary ; though this organ never empties itself, 

 it must contain a fair amount of food before rumination begins ; 

 further, it must contain a considerable quantity of fluid. If the 

 salivary flow which so largely contributes to this fluid be 

 diverted, remastication becomes difficult, though for a day or 

 two rumination may be carried on ; later it begins to fail, and 

 it is only by a great effort of the abdominal muscles that food 

 can be passed into the cesophagus. Colin's experiment in this 

 direction showed that by the thirteenth day rumination was 

 no longer possible. It has been shown that the parotids of the 

 ruminant are always in a state of activity, and the object of 

 this continuous secretion is to insure the function of rumination 

 being duly carried out. 



An animal alarmed or disturbed at once ceases to ruminate, 

 and one of the earliest signs of ill-health is that the function is 

 suspended. 



Rumination is a reflex nervous act, the centre for which 

 probably lies in the medulla. The act can only be performed 

 by means of the united action of the diaphragm, walls of the 

 stomach, and abdominal muscles. Hence, if the phrenics be 

 divided, rumination is carried out with great difficulty, and 

 only by an extra effort of the abdominal muscles ; if the vagi 

 be divided, the walls of the stomach are paralysed, and the pro- 

 cess cannot go on ; if the spinal cord be divided in the mid-dorsal 

 region, the abdominal walls are paralysed, and rumination can 

 no longer occur. 



Movements of Food in the Stomach. 



A good deal of exact information as to the manner in which the 

 stomach behaves in dealing with its contents has been obtained 

 by means of direct experimental inquiry. Colin, in the case of 



