290 REFLEX SECRETION OF SALIVA. 



tension, displacement). The movements of mastication also cause a 

 secretion of saliva. Pfliiger found that one-third more saliva was 

 secreted on the side where mastication took place ; and Cl. Bernard 

 observed that the secretion ceased in horses during the act of drinking. 

 (3) The nerves of smell, excited by certain odours. (4) The gastric 

 branches of the vagus (Frerichs, Oehl). A rush of saliva into the mouth 

 usually precedes the act of vomiting (p. 310). 



(5) The stimulation of distant sensory nerves, e.g., the central end of the sciatic 

 certainly through a complicated reflex mechanism causes a secretion of saliva 

 (Owsjannikow and Tschierjew). Perhaps the secretion of saliva, which sometimes 

 occurs during pregnancy, is caused in the same reflex manner. 



Stimulation of the conjunctiva, e.g., by applying an irritating fluid 

 to the eye of carnivorous animals, causes a reflex secretion of saliva 

 (Aschanbrandt). 



The reflex centre for the secretion of saliva lies in the medulla 

 oblongata, at the origin of the seventh and ninth cranial nerves (Eckhard, 

 Loeb). The centre for the sympathetic fibres is also placed here 

 (Griitzner and Chlapowski). This region is connected by nerve-fibres 

 with the cerebrum; hence, the thought of a savory morsel, some- 

 times when one is hungry, causes a rapid secretion of a thin watery 

 fluid [or, as we say, " makes the mouth water "]. If the centre be 

 stimulated directly by a mechanical stimulus (puncture), salivation 

 occurs, while asphyxia has the same effect. The reflex secretion of saliva 

 may be inhibited by stimulation of certain sensory nerves, e.g., by pulling 

 out a loop of the intestine (Pawlow). Stimulation of the cortex cerebri 

 of a dog, near the sulcus cruciatus, is often followed by secretion of 

 saliva (Eulenberg and Landois, Bochefontaine, Bubnoff, and Heideuhain). 

 Disease of the brain in man sometimes causes a secretion of saliva, owing 

 to the effects produced on the intracranial centre. 



So long as there is no stimulation of the nerves, there is no secretion 

 of saliva, as in sleep (Mitscherlich). Directly after the section of all the 

 nerves, secretion stops, for a time at least. 



Pathological Conditions and Poisons. Certain affections, as inflammation 

 of the mouth, neuralgia, ulcers of the mucous membrane, affections of the gums, 

 due to teething or the prolonged administration of mercury, often produce a copious 

 secretion of saliva (or ptyalism). Certain poisons cause the same effect by direct 

 stimulation of the nerves, as Calabar bean (Physostigmin), digitalin, and especially 

 pilocarpin. Many poisons, especially the narcotics above all, atropin imralyse 

 the secretory nerves, so that there is a cessation of the secretion, and the 

 mouth becomes dry ; while the administration of muscarin in this condition causes 

 secretion (Prevost). Pilocarpin acts on the chorda tympaui, causing a profuse 

 secretion, and, if atropin be given, the secretion is again arrested. Conversely, if the 

 secretion be arrested by atropin, it may be restored by the action of pilocarpin or 

 physostigmin. Nicotin, in small does, excites the secretory nerves, but in large doses 

 paralyses them (Heidenhain). Daturin, cicutin, and iodide of a;thylstrychnine, 

 paralyse the chorda. 



