VI THE SECRETION OF SALIVA 241 



In the submaxillary gland this substance is chiefly 

 mucinous, in the parotid albuminous, and some of it is 

 deposited as separate distinct granules in the body of the 

 cell (Fig. 75, A). Further it appears that during their 

 activity both glands discharge their store of material into 

 the duct leading from tliem and hence become smaller. 



But further, the submaxillary gland is supplied by a 

 nerve which is a branch of the Vllth cranial nerve (see 

 Lesson XI.) and which, since it crosses the tympanic 

 cavity or drum of the ear (.see Lesson VIII.) is called the 

 chorda tympani nerve. When this nerve is stimulated 

 tliree things happen ; the arteries which sujjply the gland 

 with blood dilate and there is a very largely increased flow 

 of blood through the gland ; the gland begins to pour out 

 its secretion ; and the cells of the gland slowly change their 

 size and appearance as already described. These changes 

 show that a good deal of the material with which they 

 were loaded during rest has been discharged. But at the 

 same time the cells have discharged a large quantity of 

 water, for saliva, like all other secretions, except the 

 secretion of the sebaceous glands (p. 197), is largely com- 

 posed of water, and this water can only have come from 

 the blood. We are thus at once face to face with the 

 question ; — has the increased supply of blood simply led 

 to an increased flow of water through the cells which has 

 carried away with it the accumulated materials of the cell- 

 substance, the whole process being largely tiltrational, or 

 has the stimulation of the nerve made the cells not only dis- 

 charge some of their substance, but also made them take up 

 water from the blood and jjass this as well through thein- 

 selves ? The answer to this question is simple and the 

 evidence in its support is conclusive. 



An increased temporary secretion may be observed on 

 stimulating the nerve even after the blood-supply to the 

 gland has been cut off, and if some drug, such as atropine, 

 be injected into the animal, then although the arteries 

 dilate to the full extent when the nerve is stimulated, no 



