THE INNERVATION OF GLANDULAR STRUCTURES 125 



containing the connector fibres connecting such cells with the 

 central nervous system. 



In addition to these secretory cells belonging to the bulbar 

 outflow, the evidence points to the conclusion that a second out- 

 flow of secretory cells to the same glands has taken place along 

 with the thoracic outflow. Stimulation of the cervical sympa- 

 thetic nerve causes a distinct secretion of saliva, especially in the 

 cat, and this secretion is accompanied by changes in the appear- 

 ance of some of the gland cells indicative of activity. According 

 to Barcroft and Piper adrenaline, when injected into the circula- 

 tion, causes a flow of saliva, which is accompanied by a dilata- 

 tion of the blood vessels of the gland and by a considerable 

 increase in the metabolism of the gland as judged by the intake 

 of oxygen. They argue that this increased metabolism cannot 

 be accounted for by the stimulation of contractile tissues in the 

 gland, for the amount of such tissue is too small to account for 

 the extent of the metabolism. They therefore conclude that 

 adrenaline produces a true secretion of the gland cells. Further 

 ergotoxine, which paralyses, as Dale has shown, all the motor 

 activities of the sympathetic system, paralyses also the secretory 

 activity of that system, but not that due to stimulation of the 

 chorda tympani ; on the other hand atropine, which stops the 

 flow of saliva obtained by stimulation of the chorda, does not 

 affect the flow due to sympathetic stimulation unless the dose is 

 very great. 



This double supply of secretory nerve fibres has been shown 

 for all the buccal secretory glands, parotid, submaxillary, sub- 

 lingual, retro-lingual, also for such glands as the orbital and 

 lacrymal ; and in all cases the secretory nerves, which belong 

 to the sympathetic system, arise from nerve cells in the superior 

 cervical ganglion. 



What is the meaning of this double innervation of these 

 glands ? I have already argued that we must, according to our 

 present knowledge, accept a double innervation of involuntary 

 muscle by motor and inhibitory fibres ; it would seem then a 

 priori natural that gland cells should possess a similar innerva- 

 tion. Heidenhain has argued that such is the case : the one 

 set of fibres (sympathetic set) he called trophic and the other 

 secretory, the trophic fibres being concerned with the formation 

 of the secretory material in the gland and the others with the act 



