DIGESTION. 187 



tliey exert a considerable pressure upon the 

 contents of the stomach ; a pressure which, no 

 doubt, tends to assist the solvent action of the 

 gastric juice. When different portions act in 

 succession, they propel the food from one part 

 to another, and thus promote the mixture of 

 every portion with the gastric juice. We often 

 find that the middle transverse bands contract 

 more strongly than the rest, and continue con- 

 tracted for a considerable time. The object 

 of this contraction, which divides the stomach 

 into two cavities, appears to be to separate its 

 contents into two portions, so that each may 

 be subjected to different processes; and, indeed, 

 the differences in structure, which are often 

 observable between these two portions of the 

 stomach, would lead to the belief that their func- 

 tions are in some respects different. 



During digestion the exit of the food from the 

 stomach into the intestine is prevented by the 

 pylorus being closed by the action of its sphinc- 

 ter muscle. It is clear that the food is required 

 to remain for some time in the stomach in order 

 to be perfectly digested ; and this closing of the 

 pylorus appears to be one means employed for 

 attaining this end ; and another is derived from 

 the proper! 3^ which the gastric juice possesses of 

 coagulating, or rendering solid, every animal or 

 vegetable fluid susceptible of undergoing that 



