92 THE INVOLUNTARY NERVOUS SYSTEM 



one case fivefold) as judged by the intake of oxygen. He con- 

 cludes from the extent of the metabolic activity that adrenaline 

 causes a true secretion of the gland, which is accompanied by a 

 marked increase of blood flow through the gland just as occurs 

 when the chorda tympani is stimulated. Is this adrenaline dilata- 

 tion to be ascribed to vaso-dilator nerves in the sympathetic, or 

 to the action of metabolic products due to the activity of the 

 gland ? 



Upon the injection of ergotoxine, Barcroft found that the sub- 

 sequent injection of adrenaline causes no rise of blood pressure, no 

 constriction of vessels in the gland, no secretion of saliva and 

 also no increase of blood flow, showing that the increase of blood 

 flow caused by the adrenaline cannot be ascribed to the stimula- 

 tion of vaso-dilator nerves, but is due to the action of meta- 

 bolites. After the ergotoxine, stimulation of the chorda tympani 

 causes a flow of saliva and a dilatation of the blood vessels, as is 

 to be expected from the nature of the action of ergotoxine. 



It seems unlikely that, if the vascular dilatation due to 

 adrenaline is not due to the stimulation of vaso-dilator fibres, 

 the similar dilatation which occurs on stimulation of the chorda 

 tympani should be due to such nerves. Barcroft has there- 

 fore investigated the evidence for metabolic activity in the 

 gland when atropine is given and then the chorda tympani 

 nerve stimulated. His researches are not yet published, but he 

 allows me to state that the dilatation of the blood vessels on sti- 

 mulation of the chorda tympani is less after atropine has been 

 given than before, and further that the intake of oxygen is in- 

 creased even though no secretion of saliva takes place. He con- 

 siders then, in agreement with Severini, that some metabolic 

 activity does take place in the gland even after atropine, and this 

 in his opinion is sufficient to produce metabolites enough to ac- 

 count for the vascular dilatation observed, without the assumption 

 of vaso-dilator nerves. 



In the case of the blood vessels of all glandular tissues it 

 cannot be said that the separate existence of vaso-dilator nerves 

 is proved without doubt. 



Let us consider now those blood vessels which supply epi- 

 thelial surfaces. As already mentioned, it has been argued that, 

 in a mixed nerve like the sciatic, the existence of vaso-dilator 

 nerves, as well as of vaso-constrictors, is shown by the methods 



