THE DIGESTIVE SECRETIONS 911 



converted into the granular substance so clearly betrayed by the resting 

 cell. In the mucous cells it has been observed that their large granules 

 swell up and disappear, probably in consequence of an inbibition of 

 water which causes the mucinogen to be converted into mucin. The 

 fact that salivary secretion is associated with such pronounced histolog- 

 ical changes cannot surprise us, if it is remembered that the submaxil- 

 lary gland of the dog secretes its own weight as saliva in the course of 

 five minutes and is able to continue this process for many hours. 



The Paralytic Secretion of Saliva. It has been found by Cl. 

 Bernard (1864) that the division of the chorda tympani innervating 

 the submaxillary gland, gives rise to a continuous secretion of saliva 

 which begins about two days after the division and persists for a period 

 of about two or three weeks. At the end of this time the gland is 

 much smaller than the one on the opposite side and exhibits a charac- 

 teristic picture of degeneration. 1 The cells are small and their nuclei 

 irregular, fragmented and deeply colored. These changes may be 

 rendered more conspicuous by the simultaneous division of the sympa- 

 thetic fibers. Obviously, we are dealing here with a trophic disturb- 

 ance in this gland which finally leads to its exhaustion. In other words, 

 in the absence of its normal innervation, the local nervous elements 

 are quite unable to effect an anabolism sufficient to compensate for 

 the catabolism resulting in consequence of some endogenous stimulus. 

 The processes of dissimilation finally gain the upper hand and cease 

 only after the secretory material has been completely exhausted. 



The Innervation of the Salivary Glands. The secretion of saliva 

 is a reflex act made possible by the existence of definite reflex circuits. 

 The center controlling this act is situated in the medulla oblongata, 

 but its boundaries have not been established with any degree of defi- 

 niteness. It is safe to assume, however, that a part of it is formed 

 by the deep origins of those nerves which participate in the innerva- 

 tion of the salivary glands, namely by the nuclei of the facial and 

 glossopharyngeal nerves. Salivation is a function apportioned to the 

 autonomic system. In last analysis, therefore, the peripheral nerves 

 controlling this process are autonomic in their character, although 

 they select typical cerebrospinal paths in gaining access to the center. 



On the efferent or motor side, the salivary center is connected with 

 the different glands by means of two separate sets of fibers, constituting 

 the so-called cerebral and sympathetic paths. The former reach the 

 glands by way of one or the other of the cranial nerves, while the latter 

 first enter the thoracic sympathetic system and then ascend in the 

 cervical sympathetic nerve. Having attained the superior cervical 

 ganglion, they follow in the course of the different arteries to their 

 respective glands. 



This arrangement may be studied most conveniently in the dog, 

 in which animal the cerebral nerve supply of the parotid is derived 



1 Maximow, Archiv fur mikr. Anat., Iviii, 1901, 1, and Gerhardt and Burton- 

 Opitz, Pfluger's Archiv, xcvii, 1903, 317. 



