THE NUTRIENTS AND NUTRITION 313 



barb-like projections at the back of the tongue serve the 

 purpose of forcing the grain toward the entrance to the gullet 

 when the tongue is moved from front to back. In water 

 fowl, the tongue is wider, softer, and more flexible. 



The salivary glands are present in the mouth of the com- 

 mon sorts of domestic birds, l>ut are imperfectly developed. 

 Shaw' recently showed that ptyalin, a starch-digesting 

 enzyme, is present in the saliva of a chick soon after hatch- 

 ing. The presence of abundant saliva is made unnecessary 

 by the fact that the feed is swallowed whole, or in quite 

 large pieces, and there is little opportunity for its action. 



Gullet and Crop. — Upon leaving the mouth the feed is 

 forced into the gullet by the tongue. The gullet (esophageal 

 canal) is distinguished by its enormous expansibihty. 

 Immediately before entering the body cavity the gullet 

 enlarges to form a pouch called the crop (ingluvies), which 

 acts as a storage for the food eaten much as does the paunch 

 of ruminants. It is into this pouch that the feed finds its 

 way. Here it becomes softened and takes on an acid re- 

 action. Although a comparatively ])rofuse secretion is 

 poured into the pouch, it contains no ferments. Its function, 

 if other than storing and softening, is not yet understood. 



Glandular Stomach. — Beyond the crop the gullet contracts 

 until well within the body cavity, when it expands somewhat 

 to form the glandular stomach (proventriculus), from which 

 it passes immediately into the gizzard (ventriculus bulbosus), 

 an involuntary sphincter muscle separating them. 



The glandular stomach, which is little more than a thick- 

 ening of the gullet wall, does not appreciably detain the feed, 

 but surrounds it with an acid gastric juice which passes with 

 it into the gizzard. It is supplied with but one type of com- 

 ])lex cells, which secrete jjcj^sin ami acid. The pepsin reduces 

 the proteid to peptones, which are further reduced by the 

 jtancreatic juice. Besides furnishing the proper medium for 

 the action of the gastric juice, the acid acts as a solvent for 

 sucli mineral matter as is not in assimilable form, thereby 

 making its absorption possible. 



' American Journal of Physiology, 1913, vol. xxxi. No. 7. 



