358 HANDBOOK OF PHYSIOLOGY. 



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 inter-tvbular capillary plexus, they open 

 finally into the venous network in the submucous tissue. 



Nerves. The nerves of the stomach are derived from the pneumogas- 

 tric and sympathetic, and form a plexus in the sub-mucous and muscular 

 coats containing many ganglia (Reuiak, Meissner). 



Gastric Juice. 



The functions of the stomach are, (;>.) to afford storage for the food 

 until it can be taken up for digestion and absorption by the intestines ; (b) 

 to secrete a digestive fluid, the gastric juice, to the action of which the 

 food is subjected after it has entered the cavity of the stomach from the 

 oesophagus ; (c) to thoroughly incorporate the fluid with the food by 

 means of its muscular movements ; and (d) to absorb such substances as 

 are ready for absorption. It is not essential to life as has been shown by 

 successful removal of the stomach ; but in such cases food has to be given 

 in small quantities frequently until a secondary dilatation of the intestine 

 has formed and can act as a place of storage. While the stomach con- 

 tains no food, and is inactive, no gastric fluid is secreted ; and mucus, 

 which is either neutral or slightly alkaline, covers its surface. But im- 

 mediately on the introduction of food or other substance, the mucous 

 membrane, previously quite pale, becomes slightly turgid and reddened 

 with the influx of a larger quantity of blood ; the gastric glands com- 

 mence 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 Beau- 

 mont was enabled, by a fortunate circumstance, to obtain it from the stom- 

 ach of a man named St. Martin, in whom there existed, as the result of 

 a gunshot wound, an opening leading directly into the stomach, near the 

 upper extremity of the great curvature, and three inches from the cardiac 

 orifice. The introduction of any mechanical irritant, such as the bulb of 

 a thermometer, into the stomach, through this artificial opening, excited 

 at once the secretion of gastric fluid. This was drawn off, and was often 

 obtained to the extent of nearly an ounce. The introduction of alimen- 

 tary substances caused a much more rapid and abundant secretion than 

 did other mechanical irritants. No increase of temperature could be de- 



