THE DIGESTIVE SYSTEM AND ITS FUNCTIONS 143 



granular and the cell outlines are very indistinct. "In one 

 . to two hours after feeding the lumina begin to be obvious, 

 and the granules to disappear from the inner border of the 

 cells. ... Up to the fifth hour these changes become 

 more and more marked, and at the same time the cells and 

 the remaining gran- 

 ules they contain 

 become distinctly 

 smaller, and the cell 

 substance stains 

 jnore deeply. . . . 

 At the period of 

 maximum change 

 the nucleus is much 

 larger compared 

 with the cell sub- 

 stance than it is dur- 

 ing rest ; it is still 

 surrounded by fine- 

 ly granular proto- 

 plasm, and it is 

 sometimes placed 

 near the outer bor- 

 der of the cells. The 

 return to the normal 

 appearance begins 

 about the fifth hour, 



A 



Fig. 40. — Showing changes in the gastric glands 

 of the frog. A, gland from a hungry frog 

 which had not been fed for five days. The 

 cell outlines are indistinct and the granules are 

 scattered throughout the cells. B, gland three 

 hours after a meal; the granules have disap- 

 peared along the inner border of the cells; 

 lumen of the gland visible. C, gland twenty- 

 five hours after a heavy meal ; the cells are 

 shrunken and not so full of granules. (After 

 Langley.) 



so that during the 



greater part of the digestive period the formative processes 

 go on whilst the secretory are still active. In twenty-four 

 hours the glands have nearly or altogether returned to the 

 hungry condition." The time and extent of the changes 

 produced in the glands were found by Langley to vary 



