334 A MANUAL OF PHYSIOLOGY 



Issuing from the cord in the anterior roots of the upper thoracic 

 nerves (first to fifth, but mainly second thoracic for the submaxillary), 

 they enter the sympathetic chain, in which they run up to the 

 superior cervical ganglion. Here they break up into terminal twigs, 

 and thus come into relation with ganglion cells, whose axis-cylinder 

 processes pass out as non-medullated fibres, and, surrounding the 

 external carotid, reach the salivary glands along its branches. 

 Langley has shown, by means of nicotine (p. 157), that the sym- 

 pathetic fibres for the submaxillary and sublingual, and, indeed, for 

 the head in general in the dog and cat, are connected with nerve- 

 cells in this ganglion, but not between it and their termination, or 

 between it and their origin from the spinal cord. 



Stimulation of the Cranial Fibres. When in the dog a 

 cannula is placed in Wharton's duct, and the saliva collected 

 (p. 376), it is found that stimulation of the peripheral end of 

 the divided chorda causes a brisk flow of watery saliva, and 

 at the same time a dilatation of the vessels of the gland, 

 which we have already described in dealing with vaso-motor 

 nerves (p. 155). That the increased secretion is not due 

 merely to the greater blood-supply, and the consequent 

 increase of capillary pressure, is shown by the injection of 

 atropia, after which stimulation of the nerve, although it 

 still causes dilatation of the vessels, is not followed by a flow 

 of saliva. Further, mere increase of pressure could not in 

 any case of itself account for the secretion, since it has been 

 found that the maximum pressure in the salivary duct when 

 the outflow of saliva from the duct is prevented may, during 

 stimulation of the chorda, much exceed the arterial blood- 

 pressure (Ludwig). In one experiment, for example, the 

 pressure in the carotid of a dog was 125 mm., in Wharton's 

 duct 195 mm. of mercury. 



Even in the head of a decapitated animal a certain 

 amount of saliva may be caused to flow by stimulation of 

 the chorda, but too much may easily be made of this. 

 And since the blood is the ultimate source of the secretion, 

 we could not expect a permanent or copious flow in the 

 absence of the circulation, even if the gland-cells could 

 continue to live. In fact, when the circulation is almost 

 stopped by strong stimulation of the sympathetic, the flow of 

 saliva caused by excitation of the chorda is at the same time 

 greatly lessened or arrested, even though the sympathetic 



