SALIVARY AND GASTRIC DIGESTION 195 



will be much reduced from its maximum size but will 

 still be pressing with little abatement of vigor upon 

 the material within. This is an unobtrusive action but 

 an important one for the success of digestion. 



The antrum is the part which, we have implied, has 

 certain affinities with a gizzard. That is to say, it has 

 a relatively high degree of muscular activity. The 

 circular muscle of its walls is rather heavily developed. 

 This muscle contracts at regular intervals, first near the 

 apparent beginning of the antrum to create a deepening 

 crease in the contour of the stomach; then other circular 

 elements successively are involved and the crease shifts 

 its position toward the pylorus. What is a crease 

 on the outside is, of course, a ring of constriction in the 

 interior. The tendency will be to force small portions 

 of the gastric contents from the stomach to the intestine. 



The waves that march down upon the pylorus in this 

 orderly fashion usually find that opening stopped by the 

 tightened condition of the muscle around it. The 

 result is that the matter which is being crowded upon 

 the pylorus slips back through the moving ring. The 

 peristaltic movement is slow but the reflux may be quite 

 brisk. It is probable that people exaggerate the energy 

 of the gastric contractions. They cannot fairly be 

 said to grind or crush the food; the verb often used is 

 " churn" and this may easily lead to a more lively 

 notion of their effect than is justifiable. The safest 

 description is conveyed by the word "mix." 



It will be recalled that the smooth muscle which 

 occurs in the walls of the stomach is to some extent 

 automatic. In fact, all the nervous connections of 

 the stomach can be broken and its behavior will be 

 approximately normal. Under such conditions the 

 movements observed are not due to muscular properties 

 alone but also to a kind of local nervous system repre- 

 sented by cells and networks of fibers in the organ 

 itself. The nerves which influence the stomach from 

 without may either increase or diminish its activity 



