. PHYSIOLOGY. 185 



immediately push the contents of the stomach into the intes- 

 tines. It seems to be the purpose of the economy to detain 

 the aliment for some time in the stomach ; and, therefore, any 

 considerable dilatation of the circular fibres, especially that 

 which occurs in a full stomach, seems to have the effect of ex- 

 citing the longitudinal fibres to a contraction, which draws the 

 two orifices of the stomach nearer to one another. By this the 

 pylorus is raised up, and rendered less easily passable, and pro- 

 bably, at the same time, the peculiar band of circular fibres 

 which surround the pylorus, are more firmly contracted, and 

 render it less pervious ( Vide CXLIV.). From hence it is, 

 that the direction of the peristaltic motion of the stomach is some- 

 times from the left to the right, and sometimes also the con- 

 trary way. It is, however, most constantly in the first manner, 

 because it is commonly begun from the oesophagus ; and be- 

 cause, when it is inverted, the resistances on the left from the 

 blind sack of the stomach, from the higher situation of the 

 cardia, and from the constriction of this by the diaphragm in 

 inspiration, are commonly more considerable than the resistance 

 at the pylorus. The contents of the stomach, therefore, are at 

 length pushed through the pylorus; in the first place, the more 

 fluid contents, as these occupy the antrum pylori, while the 

 more solid, having their air loosened by fermentation, are ren- 

 dered specifically lighter, and float nearer the upper orifice. 

 But at length, as the stomach is in any measure emptied, the 

 pylorus is less raised, is more relaxed, and allows matters to 

 pass more easily ; and, at the same time, the empty stomach 

 contracted more, is, especially towards the right extremity, con- 

 tracted to such a degree as to embrace the smallest solid mat- 

 ters now fallen down into it, and to push them through the 

 pylorus. 



This is an idea of the ordinary motions of the stomach ; but 

 they are, upon some occasions, subject to other modifications, 

 as in eructation, rumination, and vomiting, which, however, as 

 morbid, we reserve to be considered in the Pathology. 



CCXXV. The motions of the intestines will be readily un- 

 derstood from what has been said of those of the oesophagus. 

 Any portion of the intestinal canal being dilated, will in conse- 

 quence be contracted, and will urge on its contents in the same 



