rin RIOLOm OF i ii 111 



THE NORMAL SECRETION OF SALIVA 



The duel fistula can in this case he made either for tin- submaxillary 

 gland, representing a mucous gland, <>r for the parotid, representing 

 serous gland. Under ordinary conditions their i tion 



from either duet. When secretion occurs, 'u is, of course, caused by 

 influences acting mi a nerve center or centers in the medulla oblo 

 the exact location of which for the different glands has been worked nut 

 in recent years by Miller.'' The impulses acting on ii nay be 



transmitted along afferent nerves coming from the mucous membrane 



'he mouth, nares, etc., or by impulses which we may call psychic, trans- 

 mitted from tlie higher nerve centers. The refle: caused by 

 impulses traveling by the afferenl nerve from the moutl have b< 

 called unconditioned, and those from the higher nerve centei 

 Honed. With regard to the former, there is considerable discriminal 

 in the type of stimulus that will he effective. Thus, if the dog for i 

 of the experiments have been performed on this animal given m 

 a secretion of thick, mucous saliva will lie observed I ur submaxil- 

 lary gland . <>n the other hand, if the meat is dried and pulverized, 

 the secretion which it calls forth will he very copious and watery par- 

 otid gland). There is, then, an obvious association between the nature 

 of the secretion and the function it will he called upon to perform when 

 it becomes mixed with the food. The muc< sretion called forth by 

 meal will serve to Lubricate the bolus of food and thus facilil 

 swallowing, whereas the thin watery secretion produced by the dry 

 powder will have the effed of washing the powder from the mouth. 



It is evident that the mechanical condition of t l 1 partly • 



mines its exciting quality. .Mechanical stimulation of the mucosa in it- 

 self is. however, not an adequate stimulus, for if pebbh i in 

 the mouth, little secretion occurs, whereas with sand 'ion imm< 

 ately becomes copious. The nerve endings also respond t.. chemical stimuli. 

 Thus, weak acid causes a copious secretion, while alkali h 



disagreeable, nauseous substanc< 'tion. The above dif- 



ferences in the response of the glands according to the mechanii idi- 



tion of the food lias been observed in the .-.is,- of the parotid gland, 

 increase in tin- submaxillary secretion being obtained only win 



f lstulTs are placed in the mouth. 



The investigations that have been made on the condil hie 



secretion ..I' saliva are still more inten s and im] ir im- 

 portance depends not so much on the information tin • rn- 

 ing the secretion of saliva as such, as on the m 



investigating the various conditions thai 



