288 DIGESTION. 



to the action of the gastric juice. We have already noted 

 the rhythmical contractions of the lower extremity of the 

 oesophagus, by which regurgitation of food is prevented ; 1 

 and the circular fibres, which form a thick ring at the py- 

 lorus, are constantly contracted, so that, at least during the 

 first periods of digestion, only liquids and that portion of 

 food which has been reduced to a pultaceous consistence can 

 pass into the small intestine. It is well known that this re- 

 sistance at the pylorus does not endure indefinitely, for indi- 

 gestible articles of considerable size, such as stones, have 

 been passed by the anus after having been introduced into 

 the stomach ; but observation has shown that masses of 

 digestible matter are passed by the movements of the stom- 

 ach to the pylorus over and over again, and do not find 

 their way into the intestine until they have become softened 

 and broken down. 



The contractions of the walls of the stomach are of the 

 kind characteristic of the non-striated muscular fibres. If 

 the finger be introduced into the stomach of a living animal 

 during digestion, it is gently but rather firmly grasped by a 

 contraction which is slow and gradual, enduring for a few 

 seconds, and as slowly and gradually relaxing and passing to 

 another part. The movements during digestion undoubt- 

 edly present certain differences in different animals ; but 

 there can be no doubt that the phenomenon is universal, in 

 spite of the experiments of some physiologists anterior to the 

 time of Haller, who exposed the organ and always found it 

 passive. In dogs, when the abdomen is opened soon after 

 the ingestion of food, the stomach appears pretty firmly con- 

 tracted on its contents. In a case reported by Todd and 

 Bowman, in the human subject, in which the stomach was 

 very much hypertrophied and the walls of the abdomen 

 were very thin, the vermicular movements could be dis- 

 tinctly seen. These movements were active, resembling the 

 peristaltic movements of the intestines, for which, indeed, 



1 See page 204. 



