DIGESTION. 37 



from the Greek word TrvXovpbs, a porter (nvXr), a gate, and 

 ovpbs, guardian). During digestion in the stomach, the 

 pyloric orifice is closed, and afterwards, opens to allow of the 

 passage of the chyme into the intestine ; over the interior of 

 the stomach are numerous small cavities called gastric fol- 

 licles, which pour out upon the food the liquid they secrete. 



This liquid is the gastric juice, the most important of all 

 the agents of digestion, for by it the food is converted into 

 chyme. So long as the stomach is empty, it is secreted 

 only in small quantities ; but in the organ filled with food, 

 especially if solid, the gastric juice is secreted in abundance. 

 Its acid properties are always well marked. 



63. The alimentary substances which accumulate in the 

 stomach being pressed on by the muscular wall of the stomach 



Fig. 33. Stomach of the Porpoise.* 



and abdomen would reascend the gullet, but are prevented by 

 the contraction of this organ. This resistance, however, is 

 frequently overcome, as in regurgitation and vomiting. On 

 the other hand, the contraction of the pylorus during diges- 

 tion retains the food for some time in the stomach. 



64. The food thus retained is collected chiefly in the 

 part called the great cul de sac of the stomach. Some 



See "Transactions of the Koyal Society of Edinburgh." The Memoir 



Cuvier for muscular fibres. 11. K. 



