DIGESTION 



309 



a tube. The one end of this is made to open upon the skin 

 surface A, A, and, by folding in the mucous membrane, the 

 deep end is isolated from the stomach. Thus a pouch is 

 formed, still connected with the muscular coat and with the 

 nerves and the vessels of the stomach, the condition of which 

 represents the condition of the whole stomach. 



Uui culsHa 



Fig. 150. Diagram of Pavlov's Pouch made on the Stomach of a Dog. 



The condition of the stomach is very ditferent in fasting 

 and after feeding. 



A. Stomach during Fasting. 



(i.) The organ is collapsed, and the mucous membrane is 

 thrown into large ridges, (ii.) It is pale in colour because 

 the blood-vessels are not dilated. (iii.) The secretion is 

 scanty, only a little mucus being formed on the surface of 

 the lining membrane, (iv.) Movements may be absent, or 

 rhythmic contractions may occur at regular intervals of from 

 one-half to three or four minutes. These movements are 

 generally associated with the sensation of hunger, and they 

 may be called " hunger contractions." They are best marked 

 when the muscular tone of the stomach wall is good ; when 

 it is decreased by section of the vagi, they are less marked ; 



