228 OF DIGESTION. 



358. Digestion is performed principally by it. The 

 food, when properly chewed and subacted by the sa- 

 liva, is dissolved * by the gastric fluid, and converted 

 into the pultaceous chyme, so that most kinds of in- 

 gesta lose their specific qualities, are defended from 

 the usual chemical changes to which they are liable, 

 such as putridity, rancidity, &c. and acquire fresh pro- 

 perties preparatory to chylification.f (B) 



359. This important function is probably assisted by 

 various accessory circumstances. Among them, some 

 particularly mention the peristaltic motion, which, being- 

 constant and undulatory, agitates and subdues the pul- 

 taceous mass of food.;j: 



The existence of a true peristaltic motion in the sto- 

 mach during health, is, however, not quite certain ; the 

 undulatory agitation of the stomach which occurs, ap- 

 pears intended for the purpose of driving the thoroughly 

 dissolved portions downwards, while those portions 

 which are not completely subacted are repelled from 

 the pylorus by an anti peristaltic motion. 



360. The other aids commonly enumerated, are the 

 pressure on the stomach from the alternate motion of 

 the abdomen, and the high temperature maintained in 

 the stomach by the quantity of blood in the neigh- 

 bouring viscera and blood-vessels, which tempera- 

 ture was at one time supposed to be of such impor- 

 tance, that the word coction was synonymous with 

 digestion. 



* Even the stomach itself, when deprived of vitality, has been found acted 

 upon, and, as it were, digested, by it. See John Hunter, On the digestion of the 

 stomach after death. Philos. Trans. Vol. Ixii. 



f Ign.Doellinger, GrundissderNaturlehredesmenschlichen Organisnms. p. 88. 



J Wepfer, Ciciifee Aqnaticee Historia ct Noxce ; in innumerable places. 



