INFLUENCE OF NERVES ON THE SECRETION OF SALIVA. 261 



secreting cells of the glands, independent of any mediation on the part of the 

 blood-vessels. As the direct anatomical connection between the nerve-fibers and 

 the secreting cells appears proved, so, also, is the physiological connection to be 

 accepted. 



During the process of secretion the temperature of the submaxillary gland 

 rises about 1.5 C. The gland, as well as the venous blood leaving it, is not rarely 

 warmer than the arterial blood. Between the irritation of the nerve and the 

 beginning of secretion, from 1.2 to 24 seconds elapse. 



Paralytic Secretion of Saliva. By this term is understood the persistent secre- 

 tion of limpid saliva from the submaxillary gland, which sets in twenty-four hours 

 after division of the cerebral nerves, whether the sympathetic nerve is also injured 

 or is preserved. It increases for perhaps eight days; then, with degeneration of 

 the gland, it decreases. The injection of small amounts of curare into the artery 

 of the gland also produces the condition, which is prevented by apnea, while 

 dyspnea favors it. After a unilateral lesion both glands are said to take part 

 in the secretion. According to Langley, after division of the chorda tympani, its 

 central end acquires increased irritability. This exerts a centripetal effect upon 

 the salivary center on both sides. At the same time, soon after the division, a 

 ganglionic local secreting center, situated in the gland of the same side, also is 

 stimulated, so that, if all of the nerve-fibers passing to the gland are!later'separated, 

 the salivary secretion from the gland still continues. 



The Sublingual Gland. Probably the conditions existing here en- 

 tirely resemble those found in the submaxillary gland. 



The Parotid Gland. Stimulation of the sympathetic nerve alone 

 does not cause the secretion of saliva in the parotid in the dog. This 

 occurs only when the branch from the glosso-pharyngeal nerve to the 

 parotid, which is accessible in the tympanic plexus within the tympanic 

 cavity, is also stimulated at the same time. Then a viscid saliva, rich 

 in organic elements, is poured out. Stimulation of the cerebral branch 

 alone produces a clear, watery saliva, with few organic constituents, 

 but containing salivary salts. 



According to Langley, the sympathetic nerve also contains independent secre- 

 tory fibers, which can be demonstrated only by stimulation soon after the termi- 

 nation of the irritation of the tympanic nerve. After destruction of the tym- 

 panic plexus, the parotid gland atrophies. Stimulation of the glosso-pharyngeal 

 nerve in the rabbit causes secretion also in the glands of the tongue, with redness 

 of the foliate papillae. 



In the intact body excitation of the nerves causing secretion of saliva 

 occurs through reflex influences, a watery (cerebral) saliva being secreted 

 under normal conditions. The nerve-fibers conveying the impulse cen- 

 tripetally are: (i) the gustatory nerves; (2) the sensory fibers of the 

 trigeminal and glosso-pharyngeal nerves of the entire buccal cavity. 

 These seem also to cause the secretion of saliva by mechanical irritation 

 through the movements of mastication. Pfliiger found that, on the 

 side upon which mastication took place, one-third more saliva was 

 secreted. Cl. Bernard observed the secretion to cease in horses while 

 drinking. (3) The olfactory nerves, excited by certain exhalations. 

 (4) The gastric branches of the pneumogastric nerve, especially in asso- 

 ciation with strangling movements. (5) Even the irritation of distant 

 sensory nerves, such as those of the conjunctiva, by the application of 

 irritating fluids in carnivora. 



Further, stimulation of the central extremity of the divided sciatic nerve causes 

 the secretion of saliva. In this category is probably to be included also the saliv 

 tion sometimes observed in pregnant women. By irritation of distant 

 nerves both centers are excited reflexly; when nearby nerves are irritated, the 

 center on the same side is especially excited. 



