214 



REFLEX SECRETION OF SALIVA. 



"Paralytic Secretion " of Saliva. By this term is meant the continued secre- 

 tion of a thin watery saliva from the sub-maxillary gland, which occurs twenty- 

 four hours after the section of the cerebral nerves (chorda of the seventh), i.e., those 

 branches of them that go to this gland, whether the sympathetic be divided or not 

 (CI. 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. 



[Heidenhain showed that section of one chorda is followed by a continuous secretion of saliva 

 from both sub-maxillary glands. The term " paralytic" secretion is applied to that which 

 takes place on the side on which the nerve is cut, and Langley proposes to call the secretion on 

 the opposite side the antilytic. Apncea ( 368) stops both the paralytic and antilytic secretion, 

 while dyspnoea increases the flow in both cases ; and as section of the sympathetic fibres to the 

 gland (where the chorda is cut) arrests the paralytic secretion excited by dyspncea, it is evident 

 that both the paralytic secretion and the secretion following dyspnoea are caused by stimuli 

 travelling down the sympathetic fibres. In the later stages of the paralytic secretion, the cause 

 is in the gland itself, for it goes on even if all the nerves passing to the gland be divided, and 

 is probably due to a local nerve-centre. In this stage the secretion is arrested by a large dose of 

 chloroform. The paralytic secretion, in the first stage, may be owing to a venous condition of 

 the blood acting on a central secretory centre whose excitability is increased ; and in the latter 

 stages probably on local nerve-centres within the gland. The fibres of the chorda in the cat are 

 only partially degenerated thirteen days after section {Langley).'] 



[Histological Changes. In the gland during paralytic secretion, the gland-cells Of the alveoli 

 (serous, mucous, and demilunes) diminish in size and show the typical " resting " appearance, 

 even to a greater extent than the normal resting gland (Langley).'] 



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 simul- 

 taneously excited. This branch may be reached within the tympanum in the 

 tympanic plexus. A thick secretion containing much organic matter is thereby ob- 

 tained. 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. 



[Stimulation of Jacobson's Nerve (Parotid of Dog) 



Total Solids. Salts. Organic Matter. 



Without sympathetic, .... 0*56 % 0'31 0*24 



With sympathetic, 2'42 / 0*36 2'06] 



[Reflex Secretion of Saliva. If a cannula be placed in Wharton's duct, e.y., in a 

 dog, during fasting, no saliva will flow out, but on applying a sapid substance to the 



mucous membrane of the mouth or 

 the tongue, there is a copious flow 

 of saliva. If the sympathetic nerve 

 be divided, secretion still takes place 

 when the mouth is stimulated, but if 

 the chorda tympani be cut, secretion 

 no longer takes place. Hence, the 

 secretion is due to a reflex act ; in 

 this case, the lingual is the afferent, 

 and the chorda the efferent nerve 

 carrying impulses from a centre 

 situated in the medulla oblongata 

 (fig. 160).] In the intact body, the 

 secretion of saliva occurs through a 

 reflex stimulation of the nerves con- 

 cerned, whereby, under normal cir- 

 cumstances, 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 



