LETTERS TO BROTHER JOHN. 137 



with the upper extremity of the bowels is called 

 " the pylorus " : and the pylorus is furnished with a 

 peculiar valve, which accurately closes the commu- 

 nication between the stomach and bowels at all 

 times, excepting- when chyme is in the act of passing 

 out of the stomach into the bowels. This valve is 

 endowed with a singular and most beautiful kind of 

 eclectic sensibility ; which enables it to know, by 

 the feel, whether the matters which come in contact 

 with it be pure chyme or not; and nothing can 

 enter the bowels from the stomach without coming 

 in contact with it. 



Now, let us suppose that a portion of food has 

 been reduced to chyme, has flowed down to the 

 lower extremity of the stomach, and has presented 

 itself at the pyloric valve for admission through it 

 into the bowels ; and let us suppose that there is, 

 floating in the chyme, a particle of food which 

 has not yet been sufficiently acted upon by the gas- 

 tric juice. I will tell you what happens. As soon 

 as the pyloric valve feels the presence of the smooth 

 and bland chyme, it instantly opens, and allows it 

 to pass ; but no sooner does the particle of food 

 which has not yet been reduced to chyme at- 

 tempt to follow, than the valve instantly closes 

 the aperture, and refuses its permission : this par- 



