82 THE ACTIVE FORCES OF LIVING ORGANISMS 



does not warrant any definite statement. The chorda- 

 tympani, moreover, is not the only nerve which modifies 

 the vascular condition of the submaxillary gland. Fila- 

 ments reach it following the course of the small arteries 

 and proceeding from the superior cervical ganglion,* 

 whence they can be traced back along the cervical 

 sympathetic to the spinal cord, which they enter 

 presumably by the anterior roots. The function of 

 these nerves is to constrict the arteries and thus keep 

 up their tone ; but the part which they play appears 

 to be of less consequence than that of the chorda- 

 tympani, for section of the former will not prevent 

 the flow of saliva, whereas when the latter is divided 

 it ceases, and cannot be started afresh. 



Again, experimental evidence tends to show that 



the chorda-tympani nerve possesses two sets of fibres, 



one of which acts as vaso-dilators, whilst the other — 



and this is extremely important — stimulates secretion 



in the cells of the gland in a direct manner irrespective 



Direct of the blood-supply.t ' Hence,' says Foster in dealing 



«™onhe with this point, ' when the chorda is stimulated, there 



proMsses. P^'^s down the nerve, in addition to impulses affecting 



the blood-supply, impulses affecting directly the 



protoplasm of the secreting cells and calling it into 



action, just as similar impulses call into action the 



contractility of the substance of a muscular fibre.' 



These facts and others of a similar nature relating to 



other glands seem to prove conclusively that the 



* Foster, loc. cit, p. 1403. f Ibid., p. 400. 



