42 HUMAN PHYSIOLOGY 



to circulate within it and so become thoroughly 

 mixed with the secretion which the stomach pours 

 out upon it. The inner coating of the stomach, or 

 mucous layer, as it is called, is that which comes in 

 contact with the food. This mucous layer is con- 

 tinued onwards into the intestine as it appears 

 upwards in the gullet. The glands it contains 

 naturally differ according to the various functions 

 discharged at different parts of the tube. It is in 

 this mucous layer that the glands of the stomach 

 are found. These are named the gastric or peptic 

 glands, each consisting of a minute tube embedded 

 in the substance of the stomach's lining and opening 

 into the stomach by a minute aperture through 

 which the secretion of the gland is poured upon the 

 food. Again we come face to face with the work of 

 cells, for the makers of the gastric juice of the 

 stomach are microscopic cells which line the tubular 

 glands. Microscopic research has also shown that 

 the cells deep down in the glands differ from those 

 nearer the mouth of the tubes. The gastric juice 

 each gland secretes therefore seems to undergo a 

 process of elaboration as it advances from the lower 

 part of the tube until it is poured into the stomach. 

 GASTRIC JUICE. The gastric juice of the stomach 

 is a fluid of much importance. It exercises, as we 

 shall see, a very definite action upon certain foods. 

 We find it to consist of water, minerals (amongst 

 which common salt bulks somewhat largely), an acid 

 called hydrochloric acid, and a special ferment found 

 in no other secretion of the body and known as 

 pepsin. The digestive action of gastric juice is no 

 doubt specially due to the action of the pepsin and 

 the acid, but at the same time we cannot afford to 

 ignore the part which may be played in such action 



