EXTERNAL DIGESTIVE SECRETIONS 



93 



In the second digestive period (which includes the interval 

 between 10 and 20 hours after the meal) the alveoli increase in 

 bulk by a marked enlargement of the secretory cells. Their 



FIG. 31. Dog's pancreas, excised during second period of digestion. 

 Alcohol-carmine method. (Heidenhain.) 



inner zone is much enlarged, while the outer is more reduced 

 than it was during fasting ; their nuclei are no longer round, but 

 flat and angular (Fig. 31). From all this Heidenhain concludes 

 that the inner zone of cells is consumed or dissolved during the 



FIG. 32. Two alveoli from pancreas of living rabbit, in state of rest and of secretory activity. 

 (Kiilme and Sheridan Lea.) A, resting state ; B, after secretion. 



first stage of digestion, and regenerated at the expense of the 

 outer zone in the second, as if the one were transformed into 

 the other. 



The later researches of Kiihne and Lea, obtained by direct 

 observations on live rabbits, have corrected Heidenhain's observa- 

 tions in accordance with the earlier doctrine of Johannes Mliller. 



