438 DIGESTION. 



of the mouth causes no reflex excitation of the secretory nerves of the 

 stomach. There are two moments which cause a secretion, namely, 

 the psychical moment the passionate desire for food and the sensation 

 of satisfaction and pleasure on partaking it and the chemical moment, 

 the action of certain chemical substances on the mucous membrane of 

 the stomach. The first moment is the most important. The secretion 

 occurring under its influence by the vagus fibers appears earlier than that 

 produced by chemical irritants, but only after an interval of at least 

 4^ minutes. This secretion is more abundant but less continuous than 

 the " chemical." It yields a more acid and active juice than the latter. 

 As chemical excitants which cause a secretion reflexively through the 

 stomach mucosa we include water (slight action) and certain unknown 

 extractive substances contained in meat and meat extracts, in impure 

 peptone, and also, it seems, in milk. According to HERZEN and RAD- 

 ZIKOWSKI 1 and others, alcohol is also a strong agent in producing a flow 

 of juice. The claims in regard to the action of sodium chloride and 

 alkali carbonates are somewhat disputed. That the alkali carbonates 

 retard or inhibit secretion is the opinion of many, but from recent deter- 

 minations 2 it would seem as if the concentration of the carbonate as well 

 as of sodium chloride exercises a certain influence, so that a weaker con- 

 centration is indifferent or retarding, while somewhat stronger concen- 

 tration has an accelerating action upon secretion, though investigators 

 are not agreed as to results. Bitter substances partaken of in small 

 amounts a certain time before a meal increase the secretion, while larger 

 amounts have a retarding action (Bomssow, STRASHESKO 3 ) . Fats 

 have a retarding action on the appearance of secretion and diminish the 

 quantity of juice secreted as well as the amount of enzyme. The sub- 

 stances, such as egg-albumin, which act as chemical stimulants, cannot 

 be digested by the " psychical " secretion, but may perhaps cause a chem- 

 ical secretion by their decomposition products. 



The quantity of juice secreted during digestion is proportional to the 

 quantity of foody and the secretion of gastric juice may also be influenced 

 by the kind of food. This action of various foods meat, bread, and 

 milk may be arranged in progressive series as follows: 



1 Pfliiger's Arch., 84, 513. 



2 See Rozenblatt, Bioch. Zeitschr., 4; Mayeda, ibid., 2; Pimenow, Bioch. Centralbl., 

 6; Lonquist, Maly Jahresb., 36. 



3 Borissow, Arch. f. exp. Path. u. Pharm., 51; Strashesko, see Biochem. Centralbl., 

 4, 148. 



