250 HANDBOOK OF PHYSIOLOGY. 



ening reagent; for if examined during life they appear to be confined 

 to the inner zone of the cells, and the outer zone is free from granules, 

 whereas during rest the cell is granular throughout. These granules are 

 thought to be pepsin, or the substance from which pepsin is formed, 

 pepsinogen, which is during rest stored chiefly in the inner zone of the 

 cells and discharged into the lumen of the tube during secretion. (Lang- 

 ley.) 



Lymphatics. Lymphatic vessels surround the gland tubes to a 

 greater or less extent. Towards the fundus of the peptic glands are 

 found masses of lymph oid tissue, which may appear as distinct follicles, 

 somewhat like the solitary glands of the small intestine. 



Blood-vessels. The blood-vessels of the stomach, which first break 

 up in the submucous tissue, send branches upward between the closely 

 packed glandular tubes, anastomosing around them by means of a fine 

 capillary network, with oblong meshes. Continuous with this deeper 

 plexus, or prolonged upwards from it, so to speak, is a more superficial 

 network of larger capillaries, which branch densely around the orifices 

 of the tubes, and form the framework on which are moulded the small 

 elevated ridges of mucous membrane bounding the minute, polygonal 

 pits before referred to. From this superficial network the veins chiefly 

 take their origin. Thence passing down between the tubes with no very 

 free connection with the deeper intertubular capillary plexus, they open 

 finally into the venous network in the submucous tissue. 



Nerves. The nerves of the stomach are derived from the pneu mo- 

 gastric and sympathetic, and form a plexus in the submucous and mus- 

 cular coats, containing many ganglia (Eemak, Meissner). 



Gastric Juice. 



Gastric Juice. The functions of the stomach are to secrete a digest- 

 ive fluid (gastric juice), to the action of which the food is subjected after 

 it has entered the cavity of the stomach from the oesophagus; to thor- 

 oughly incorporate the fluid with the food by means of its muscular 

 movements; and to absorb such substances as are ready for absorption. 

 While the stomach contains no food, and is inactive, no gastric fluid is 

 secreted; and mucus, which is either neutral or slightly alkaline, covers 

 its surface. But immediately on the introduction of food or other sub- 

 stance the mucous membrane, previously quite pale, becomes slightly 

 turgid and reddened with the influx of a larger quantity of blood; the 

 gastric glands commence secreting actively, and an acid fluid is poured 

 out in minute drops, which gradually run together and flow down the 

 walls of the stomach, or soak into the substances within it. 



Chemical Composition. The first accurate analysis of gastric juice 

 was made by Prout: but it does not appear to have been collected in any 

 large quantity, or pure and separate from food, until the time when 



