Sympathetic Innervation 59 



probable that section of the chorda affects cells which can be influ- 

 enced by the sympathetic also, i.e. cells with a double innervation. 

 Similarly, removal of the superior cervical ganglion sensitizes the 

 gland cells to acetylcholine and to impulses of low frequency in 

 the chorda. Cross-suture experiments have, likewise, pointed to the 

 existence of a double innervation (Emmelin, Muren and Strom- 

 blad, 19570 and b). When hypoglossal fibres were made to inner- 

 vate the submaxillary gland through the chorda, the supersensitivity 

 to drugs which developed when the chorda was cut was found to 

 decrease. When, instead, the hypoglossal nerve was connected to 

 the cervical sympathetic trunk and the chorda cut, the super- 

 sensitivity was also found to decrease when there was evidence 

 of a functional union, for instance when swallowing movements 

 were accompanied by dilatation of the pupil, retraction of the 

 nictitating membrane and secretion of saliva. The hypoglossal 

 nerve is thus not only able to counteract the supersensitivity, fol- 

 lowing section of the chorda, when connected to the chorda, but 

 to the sympathetic as well. This surely suggests that the chorda 

 and the sympathetic act on the same gland cells. 



There are thus several very different types of experiments sup- 

 porting the view that the gland cells of at least many salivary glands 

 have a double innervation. On these particular structures the two 

 divisions of the autonomic nervous system have consequently not 

 an antagonistic function ; in the salivary glands the antagonism is 

 exerted on the vascular bed only. The two sets of nerves act rather 

 synergistically, as seen in the "true augmented secretion". This 

 does by no means imply that the nerves have identical effects on the 

 secretory cells. Saliva secreted under the influence of one nerve 

 may differ very much in its composition from a sample collected 

 during stimulation of the other nerve, and the difference cannot 

 be due to vascular factors alone. Furthermore, the electrical 

 responses to the two types of nerves are very different, in the 

 "type 2" responses of Lundberg even of different sign. 



The picture of a salivary cell is thus that of a cell which can be 

 excited by two different transmitters, both causing graded responses 

 according to their concentration; the action of one substance is 

 specifically antagonized by drugs like atropine, that of the other by 

 drugs like ergotamine ; and the response of the cell to one trans- 

 mitter can be very different from that to the other one. 



The chemical transmitter responsible for the secretory effects of 



