146 THE BIOLOGY OF THE FROG chap. 



portion of the cell goes on so that a clear zone is formed. 

 The clear zone steadily increases until the sixth to twelfth 

 hour, or even later, the time varying with the state of the 

 animal and the amount of food given. The glands then 

 begin to become more granular, the time of complete 

 recovery varies enormously : in some cases the glands are 

 throughout granular in twenty-four hours from the time of 

 feeding the animal, in others they do not become so for 

 several days." 



If the frog is fed with pieces of sponge instead of food, a 

 secretion is set up both in the stomach and the esophagus, 

 the change being as a rule the greater, the larger the sponge. 

 Similar changes take place in the cells to those produced by 

 digestible food, but they occur much more slowly, beginning 

 generally only three or four hours after the sponge is placed 

 in the stomach ; the granules begin to increase again in the 

 esophagus only after some days. 



Nussbaum has found that a direct stimulation of a partic- 

 ular part of the mucous membrane of the esophagus causes 

 a disappearance of the granules from that region. The con- 

 clusions of Nussbaum that in normal hungry frogs the cells of 

 the esophageal glands have an outer clear zone, and that 

 after feeding there is an increase instead of a decrease of 

 granules, were probably drawn from unhealthy specimens. 

 Sluggish and unhealthy frogs often show glandular cells with 

 an outer clear zone, but lively and vigorous specimens have 

 the cells filled with granules. Hungry frogs with foreign 

 bodies in the stomach, such as bits of leaf or other objects 

 swallowed with the food, often show a decrease in the granu- 

 lar content of the gland cells, owing to the irritation thus set 

 up. According to Grlitzner there is a preliminary increase in 

 the granules in the esophageal glands for a short time after 

 feeding, and then a marked decrease, but Langley was able 



