58 



PHYSIOLOGY FOR NURSES 



ond to coagulate the albumin of milk. In addition about 

 five-tenths of one per cent of gastric juice is hydro- 

 chloric add, a strong mineral acid which promotes the 

 activity of pepsin. 



Mechanism of Secretion. The mere smell or taste of 

 appetizing food is enough to start gastric secretion and, 

 indeed, seems to be its normal stimulus. Some foods, 

 however, appear to contain substances called secreto- 

 gogucs, which continue to excite secretion after intro- 

 duction into the stomach. Meat extracts and juices ap- 



Fig. 13. Schema of simple reflex arc: r, receptor in an epithelial mem- 

 brane; a, afferent fiber; s, synapsis; c, nerve cell of center; e, efferent fiber; 

 in, effector organ. (Pearce-Macleod, Fundamentals of PI it man Physiology.) 



pear to possess these substances in a high degree, while 

 they seem almost absent from bread and white of egg 

 and present in but small quantity in milk. 



Pepsin can not act in an alkaline solution and acts best 

 in the presence of hydrochloric or other mineral acid. It 

 acts on protein alone which it finally converts into pep- 

 tones, a soluble protein more ready for absorption than 

 pure protein. There are intermediate steps before the 



