VII THE DIGESTIVE SYSTEM AND ITS FUNCTIONS 145 



it is then only with difificulty that the mucous can be dis- 

 tinguished from the subcubical cells." 



The changes undergone by the esophageal glands differ 

 somewhat from those of the glands of the stomach. Langley 

 and Sewall, and also Grutzner, found that in normal hungry 

 frogs the cells were granular throughout. Some time after 

 food is taken the granules begin to disappear near the outer 

 end of the cell ; i.e. the end away from the lumen of the 

 gland instead of in the opposite end as in the gastric glands. 

 The outer clear zone thus produced increases in size as 

 digestion proceeds, and the whole cell grows smaller. " As 

 the outer zone increases, the granules in the inner end 

 become smaller. The diminution in the size of the granules 

 is very marked in cells in which the outer zone takes up the 

 larger part of the cell. . . . Nothing very definite can be said 

 as to the time after feeding at which the changes in the 

 esophageal glands occur. When frogs are taken as nearly 

 as possible alike, and they are treated in the same way, then 

 the results obtained correspond very closely ; but when such 

 results are compared with those obtained from frogs which 

 are older or younger, more or less healthy, or when different 

 amounts of food are given, then considerable divergences 

 occur." 



■ "The changes occurring are in each case of the same 

 nature, but the extent to which these changes take place 

 varies largely. Hence any estimation made of the time 

 taken for the first appearance of a clear zone, for its maxi- 

 mum development, and so on, can only be approximate." 



" During the first hour and a half after feeding no distinct 

 change is to be seen. After this period a diminution in the 

 number of granules in the outer half of the cell becomes 

 obvious. Usually this is first seen in the glands close to 

 the stomach. The disappearance of granules in the outer 



