REFLEX SECRETION OF SALIVA. 



289 



sympathetic be divided or not (Cl. Bernard). It increases until the 

 eighth day, after which it gradually diminishes, while the gland tissue 

 degenerates. The injection of a small quantity of curara into the artery 

 of the gland also causes it. Perhaps it arises from the secretion, which 

 stagnates within the gland after section of the nerves, acting as a direct 

 stimulus to secretion (Heidenhain). Perhaps it may be explained as a 

 degeneration effect, comparable to the fibrillar contractions which occur 

 in a muscle after secretion of its motor nerve. 



B. Sub-lingual Gland. Very probably the same relations obtain as 

 in the sub-maxillary gland. 



C. Parotid Gland. In the dog, stimulation of the sympathetic alone, 

 causes no secretion ; it occurs when the glosso-pharyngeal branch to the 

 parotid is simultaneously excited. This branch may be reached within 

 the tympanum in the tympanic plexus. A thick secretion containing much 

 organic matter is thereby obtained. Stimulation of the cerebral branch 

 alone yields a clear thin watery secretion, containing a very small amount 

 of organic substances, but a considerable amount of the salts of the 

 saliva (Heidenhain). 



Reflex Secretion of Saliva. [If a cannula be placed in Wharton's 

 duct, e.g., in a dog, during fasting, no saliva will flow out. If the mu- 

 cous membrane of the mouth be stimulated by a sapid substance placed 

 on the tongue, there is a copious flow of saliva. If the sympathetic 

 nerve be divided, secre- 

 tion still takes place when 

 the mouth is stimulated, 

 but if the chorda tympani 

 be cut, secretion no longer 

 takes place. Hence, the 

 secretion is a reflex act ; 

 in this case, the lingual 

 is the afferent, and the 

 chorda the nerve-carry- 

 ing impulses from a 

 centre situated in the 

 medulla oblongata (Fig. 

 120).] In the intact body, 

 the secretion of saliva 



Diagram of a salivary gland. 



occurs through a reflex stimulation of the nerves concerned, whereby 

 under normal circumstances the secretion is always watery (chorda or 

 facial saliva). The centripetal or afferent nerve-fibres concerned are: 

 (1) The nerves of taste. (2) The sensory branches of the trigeminus 

 of the entire cavity of the mouth and the glosso-pharyngeal (which 

 appear to be capable of being stimulated by mechanical stimuli, pressure, 



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