ii EXTEBNAL DIGESTIVE SECEETIONS 79 



differs widely from that described by Heidenhain, it lends itself 

 essentially to the same interpretation. 



In the serous glands, Langley found that in the resting state 

 the secretory cells exhibit a protoplasm rich in granules, which 

 conceal the outline of the cells and the nuclei. After prolonged 

 secretion, caused either by injection of pilocarpine or by stimulation 

 of the nerve, the alveoli become smaller, and the granules gradually 

 disappear, especially in the outer zone which is covered by the 

 basement membrane ; they collect in the inner zone, which 

 surrounds the lumen, and finally vanish, accumulating as secretion 

 in the cavities of the gland (Fig. 23). 



Similar phenomena can be observed in fresh preparations of 

 the mucous glands. They are more conspicuous in the simple 

 than in the compound glands, 

 e.g. those of the frog's tongue, 

 placed as soon as excised in 

 physiological salt solution 

 (Biedermann). In the rest- 

 ing state the cells are full 

 of dark, highly refracting 

 granules, which often conceal 

 the nucleus ; during active 

 secretion, on the contrary, the 

 granulation practically disap- 



11, . FIG. 24. Part of lingual gland of Rana esculenta, 



pears, and Wliat remains IS in fresh state. (Biedermann.) A, resting state; 



collected at the inner margin ^KSS?**^ f gloss - phar y n s eal nerve 

 (Fig. 24). -r 



From these data we learn that a substance is formed during 

 the functional rest of both albuminous and mucous salivary glands 

 which disappears during activity, and passes into the secretion, 

 while the cell becomes swollen. This substance dissolves 

 in alcohol -hardened, carmine - stained preparations; in fresh 

 specimens, on the contrary, it appears in the form of small 

 granules. 



These phenomena do not decide the important question 

 whether during the secretory process the living protoplasm of the 

 cells is utilised and converted into the materials of secretion, or 

 whether the secretion is produced by the living protoplasm as a 

 direct elaboration of the lymph absorbed from the perialveolar 

 lymph spaces. Heidenhain adopted the former view, and con- 

 cluded that the cells liquefy in consequence of their secretory 

 activity. According to him Giannuzzi's demilunes consist of cells 

 intended to replace those which break up. Against this theory is 

 the fact that karyokinesis is rarely seen during secretion, and that 

 if epithelial regeneration be present, it relates not to secretory 

 activity, but to the life cycle of the individual cells. The second 

 theory, which, as we have seen, was held by Johannes Mliller, and 



