DIGESTION OF POOD. 



311 



SECRETION AS A PHYSIOLOGICAL PROCESS. 



Secretion of the Salivary Glands.— We shall treat this subject 

 at more length because of the light it throws on the nervous 

 phenomena of vital process ; and, since the salivary glands have 

 been studied more thoroughly and successfully than any other, 

 they vfill receive greater attention. 



Pig. 253. 



Fio. 254. 



Pig. 253.— liObale of parotid gland, injected with mercury, and magniaed 50 diame- 

 ters. 

 Pig. 254.— Capillary network around the follicles of the parotid gland. 



The main facts, ascertained experimentally and otherwise, 

 are the following : 



Assuming that the student is familiar with the general ana- 

 tomical relations of the salivary glands in some mammal, we 

 would further remind him that the submaxillary gland has a 

 double nervous supply : 1. From the cervical sympathetic by 

 branches passing to the gland along its arteries. 2. From the 

 chorda tympani nerve, which after leaving the facial makes 

 connection with the lingual, whence it proceeds to its desti- 

 nation. 



The following facts are of importance as a basis for conclu- 

 sions: 1. It is a matter of common observation that a flow of 

 saliva may be excited by the smell, taste, sight, or even thought 

 of food. 2. It is also a matter of experience that emotions, as 

 fear, anxiety, etc., may parch the mouth — i. e., arrest thg flow 

 of saliva. The excited speaker thus suffers in his early efforts. 

 3. If a glass tube be placed in the duct of the gland and any 

 substance that naturally causes a flow of saliva be placed on 

 the tongue, saliva may be seen to rise rapidly in the tube. 4. 

 The same may be observed if the lingual nerve, the glossopha- 



