772 PHYSIOLOGY OF DIGESTION AND SECRETION. 



nerve centers concerned must lie in the stomach itself, the reflex 

 must take place through the intrinsic ganglion cells. Another 

 more probable explanation has been offered. Edkins * has shown 

 that decoctions of the pyloric mucous membrane, made by boiling 

 in water, acid or peptone solutions, when injected into the blood 

 cause a marked secretion of gastric juice. These substances when 

 injected alone into the blood cause no such effect, and decoctions 

 of the mucous membrane of the fundic end of the stomach are 

 without action on the gastric secretion. This author suggests, 

 therefore, that the secretagogues, whether preformed in the food or 

 formed during digestion, act upon the pyloric mucous membrane 

 and form a substance which he designates as gastrin or gastric se- 

 cretin, and this substance after absorption into the blood is carried 

 to the gastric glands and stimulates them to secretion. The effect 

 is, therefore, not a usual nervous reflex, but an instance of the 

 stimulation of one organ by chemical products formed in another. 

 Starling t has emphasized the fact that this mode of control is 

 frequently employed in the body, as will be described in the 

 following pages in connection with the pancreatic secretion and 

 the internal secretions. He proposes to designate such substances 

 by the general term of hormones (from dp/iaco, arouse or excite). 

 Later workers | state that gastrin may be obtained by extraction 

 with 0.4 per cent. HCl from the mucous membrane of all parts of 

 the stomach. The chemical nature of the gastrin has not been 

 determined definitely, but it seems to be a basic body containing 

 an iminazol grouping and related in structure to histamine (/?-im- 

 inazolethylamine) . Leaving aside for the moment the way in 

 which the secretagogues excite the secretion it is important to em- 

 phasize the fact that in the normal secretion of gastric juice, that 

 is to say, in the secretion which takes place during an ordinary 

 meal, we must distinguish between a nervous secretion due to 

 the action of the secretory fibers in the vagus, and a chemical 

 secretion due to the chemical stimulation of the secretagogues or 

 of the hormones produced by them. 



The researches of Pawlow and his co-workers seem also to in- 

 dicate that the quantity and properties of the secretion vary with 

 the character of the food. The quantity of the secretion varies, 

 also, other conditions being the same, with the amount of food to 

 be digested, and, so far as the psychical or appetite secretion is 

 concerned, with the palatableness of the food. The apparatus 

 is adjusted in this respect to work economically. Different 

 kinds of food produce secretions var3dng not only as regards 



* Edkins, "Journal of Physiology," 1906, xxxiv, p. 133. 

 t Starling, "Recent Advances in the Physiology of Digestion," 1906. 

 X Koch, Luckhardt, and Keeton, "American Journal of Physiology," 52, 

 508, 1920. 



