170 PHYSIOLOGY CHAP. 



muscles ; in the vagi ami spinal accessory for the muscles of the 

 palate, pharynx, and oesophagus. 



The cardia belongs by its movements to the oesophagus, its 

 function being co-ordinated witli the swallowing movements in 

 the latter ; it contracts after the last part of the oesophagus, and 

 loses its tonicity when the oesophagus is relaxed under the 

 inhibitory influence of the glosso-pharyngeal nerves. 



V. On reaching the stomach the alimentary boluses remain 

 there for several hours, according to the nature of the food, and 

 suffer various changes of a chemical character. The importance of 

 the stomach was formerly exaggerated, since it was held to be the 

 centre of the digestive system ; and the mass of the food-stuffs 

 transformed by it was known as chyme, meaning by this term 

 a pulp differing far more in constitution from the raw materials 

 ingested than it does in reality. As it became recognised that 

 the action of the gastric juice is almost entirely confined to 

 protein, and that even this property is not limited to the stomach 

 but is common to the intestine also, a more reasonable conception 

 prevailed of the functional value of this viscus. The fact that 

 food remains a long time in the stomach is not enough to give it 

 a predominating importance in digestion. The surface of the 

 stomach being relatively small in comparison with the ample 

 surface of the intestine, while it secretes an acid peculiar to itself, 

 it would be necessary (in order that the gastric juice may act 

 effectively) to compensate the limited surface of the organ by a 

 prolonged stay of the food within it. It has, on the contrary, been 

 proved, as we shall see, that food remains longer in the small 

 intestine as a whole than it does in the stomach. Lastly, it is 

 important to note that surgeons (Czerny, Kaiser and others) have 

 succeeded in keeping dogs and man in good condition for mouths 

 and even years after the excision of practically the whole of the 

 stomach. These facts show that the stomach is in no sense 

 absolutely essential to life. In another connection we shall 

 analyse the details and effects of the operation. 



Two methods are employed to study the digestive action of the 

 gastric juice : that of natural digestion, which consists in observ- 

 ing the changes the food undergoes in the stomach (when intro- 

 duced in muslin bags by fistula) ; and that of artificial digestion in 

 vitro, in which the various foods are brought into contact with 

 natural or artificial gastric juice, at a proper temperature. The 

 first method, inaugurated by Beaumont, serves to give an idea of 

 the process as a whole ; the second, instituted by Eeaumur and 

 Spallanzani, yields a minute analysis of the different phases of the 

 process and the various products resulting from it. 



It is easy with artificial digestions to show that the funda- 

 mental digestive action of the gastric juice consists in the so- 

 called peptonising of the proteins, by which these substances, 



