140 LETTERS TO BROTHER JOHN. 



rible. My mind's eye aches with looking at it. 

 Above all things, my dear John, take care of your 

 pyloric valve ! 



Now let us get on a step further. 



The food having been thoroughly and properly 

 acted upon by the gastric juice in the stomach, is re- 

 duced to a uniform substance, called "chyme"; and 

 this is the first great change in that succession of 

 changes which is ultimately to convert it into blood. 

 There is now neither bread nor meat in your sto- 

 mach, there is nothing there but chyme; which 

 is neither meat nor bread ; but a fluid, the nature 

 of which is one degree nearer to the nature of blood 

 than it was before it became so. 



The chyme then flows to the lower extremity 

 of the stomach ; presents itself at the pyloric valve ; 

 and, having been examined, as it were, by the SEN- 

 SIBILITY of that valve, and reported " all right," is 

 admitted into the duodenum. 



The first twelve inches of the bowels, reckoning 

 from their junction with the stomach downward, 

 are called the duodenum. 



Now, the chyme in the duodenum has precisely 

 the same effect upon the excretory ducts of the 

 liver and pancreas, which open into the duodenum, 

 as the food had, in the mouth, upon the excretory 



