180 PHYSIOLOGY OF ALIMENTATION. 



secretion of saliva has occurred in a gland shortly after stimu- 

 lation, as evidenced by the presence of saliva in the smaller 

 ducts of the gland, external evidence, that is a movement of 

 saliva in the glass catheter inserted into the duct of WHARTON, 

 STENSON, or BARTHOLIN, is not so readily obtained. Such a 

 movement is discoverable only after stimulation has been 

 continued for some time and not witkin a few seconds, as 

 when the cranial nerves are stimulated. LANGLEY has calcu- 

 lated that at the best only 1/30 to 1/60 of the quantity of 

 saliva which would be obtained from the submaxillary gland 

 were the chorda tympani stimulated is obtained when the 

 sympathetic fibres of the same gland are stimulated. 



In contrast to the clear watery saliva obtained through 

 stimulation of the cranial fibres, that obtained when the 

 sympathetic fibres of one of the salivary glands is stimu- 

 lated is turbid, thick, and ropy. While in such sympa- 

 thetic saliva great variations in chemical composition are 

 also found in different animals, it can be said in general 

 that it is much richer in organic and inorganic material 

 than is cranial saliva, containing as it does on an average 

 of from 3 to 4 percent solids. 



Various attempts have been made to explain these differ- 

 ences in the chemical composition of the various salivas 

 and in the quantities secreted. The nerves have been 

 charged with a multiplicity of functions, but none of these 

 explanations can as yet be regarded as satisfactory. 



Stimulation of the nerves supplying a salivary gland is 

 accompanied by a series of accessory phenomena which 

 deserve notice. When induction shocks are applied to the 

 chorda tympani nerve, for example, not only does the rate 

 of salivary secretion increase, but the gland swells, becomes 

 redder in color, and the efferent veins pulsate with arterial 

 blood. The chorda tympani, in other words, carries vaso- 

 motor nerves to the gland. It 'was once thought that the 

 increased secretion of saliva was due to this increased flow 

 of blood through the gland, but this can no longer be held. 



