REFLEX SECEETION OF SALIVA. 21 5 



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

 secretion of saliva. Pfluger found that one-third more saliva was secreted on the 

 side where mastication took place ; and CI. 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. A rush of saliva into the 

 mouth usually precedes the act of vomiting ( 158). 



(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). Stimulation of the conjunctiva, e.g., by applying an irritating fluid to the eye of 

 carnivorous animals, causes a reflex secretion of saliva (Aschenbrandt). Perhaps the secretion 

 of saliva which sometimes occurs during pregnancy is caused in a similar reflex manner. 



(6) The movements of mastication excite secretion, but although, during the act of rumination; 

 this is the case in ruminants, in whom the process of mastication is very thorough, there is no 

 secretion from the sub-maxillary gland, although the parotid secretes (Colin, Ellenberger and 

 Eofmeister). 



The reflex centre for the secretion of saliva lies in the medulla oblongata, at 

 the origin of the seventh and ninth cranial nerves. The centre for the sympa- 

 thetic fibres is also placed here. This region is connected by nerve-fibres 

 with the cerebrum J hence, the thought of a savoury morsel, sometimes, 

 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. Stimulation of the cortex 

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

 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. Immediately after the section of all nerves, secretion stops, for a time 

 at least. 



Pathological Conditions and Poisons. Certain affections, as inflammation of tne mouth, 

 neuralgia ; ulcers of the mucous membrane, and 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 paralyse 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. 

 Pilocarpin acts on the chorda tympani, 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, doses,, excites the 

 secretory nerves, but in large doses paralyses them. Daturin, cicutin, and iodide of sethylstrych- 

 nin, paralyse the chorda. The saliva is diminished in amount in man, in cases of paralysis of 

 the facial or sympathetic nerves, as is observed in unilateral paralysis of these nerves. 



[Sialogogues are those drugs which increase the secretion of saliva. Some are topical, and 

 take effect when applied to the mouth. They excite secretion reflexly by acting on the sensory 

 nerves of the mouth. They include acids, and various pungent bodies, such as mustard, ginger, 

 pyrethrum, tobacco, ether, and chloroform ; but they do not all produce the same effect on the 

 amount or quality of the saliva ; others, the general sialogogues, cause salivation when intro- 

 duced into the blood ; physostigmin, nicotin, pilocarpin, muscarin. The drugs named act after 

 all the nerves going to the gland are divided, so that they stimulate the peripheral ends of the 

 nerves in the glands. The two former also excite the central ends of the secretory nerves.] 



[Anti-sialics are those substances which diminish the secretion of saliva, and they may take 

 effect upon any part of the reflex arc, i. e. , on the mouth, the afferent nerves, the nerve-centre 

 and afferent nerves, or upon the blood-stream through the glands, or on the glands themselves. 

 Opium and morphia affect the centre, large doses of physostigmin affect the blood-supply, but 

 atropin is the most powerful of all, as it paralyses the terminations of the secretory nerves in 

 the glands, e.g., the chorda tympani, and even the sympathetic in the cat (but not in the 

 dog).] 



