764 



PHYSIOLOGY OF DIGESTION AND SECRETION. 



glands secreting the gastric juice (gastric secretin or gastric hor- 

 mone).* 



Histological Changes in the Gastric Glands during Secretion. — 



The cells of the gastric glands, especially the so-called central cells, 

 show distinct changes as the result of prolonged activity. Upon 

 preserved specimens, taken from dogs fed at intervals of twenty- 

 four hours, Heidenhain found that in the fasting condition the 

 central cells were large and clear, that during the first six hours of 

 digestion the central cells as well as the border cells increased in 



■t*^ 



Fig. 293. — Glands of the fundus (dog): A and A^, during hunger, resting condition; 

 B, during the first stage of digestion; C and D, the second stage of digestion, showing 

 the diminution in the size of the "chief" or central cells. — (After Heidenhain.) 



size, but that in a second period, extending from the sixth to the 

 fifteenth hour, the central cells became gradually smaller, while 

 the parietal cells remained large or even increased in size. After 

 the fifteenth hour the central cells increased in size, gradually 

 passing back to the fasting condition (see Fig. 293). 



Langleyt has succeeded in following the changes in a more satis- 

 factory way by observations made directly upon the living gland. 



* See Starling, "Physiology of Secretion," Chicago, 1906, and Edkins, 

 "Journal of Physiology," 1906, xxxiv., 133. 

 t "Journal of Physiology," 3, 269, 1880. 



