INHIBITORY NERVES TO THE VASCULAR SYSTEM 91 



pani no longer caused secretion in the submaxillary gland when 

 atropine had been given, and Heidenhain pointed out that, even 

 after atropine, stimulation of the nerve still caused an increased flow 

 of blood through the gland ; he therefore stated that fibres which 

 caused the dilatation of tl^e blood vessels existed in the chorda tym- 

 pani independently of those which caused secretion; in other words, 

 vaso-dilator nerves existed apart from glandular nerves. The 

 same argument applies to other cases of glandular activity such 

 as the parotid gland, noticed by Loeb and Eckhard, and the 

 lingual glands. Severini has raised doubts of the validity of 

 this reasoning, for he says that, even although atropine may pre- 

 vent any external secretion through the ducts, it does not follow 

 that it prevents all internal secretion into the blood and lymph 

 fluids when the nerve is stimulated, and indeed he asserts that 

 changes can be observed in the microscopic structure of the 

 gland cells, even in the gland under atropine, when the chorda 

 tympani is stimulated. Further these so-called vaso-dilator 

 fibres, like the corresponding ones of muscle, are always in all 

 parts of their course associated with the fibres which cause the 

 activity of the organ. 



Of recent years Barcroft has investigated the metabolism 

 of the cells of the submaxillary gland under different conditions, 

 by the estimation of the amount of oxygen taken in ; and he 

 has found that, coincident with the secretion of saliva and the in- 

 creased blood flow through the gland, there may be as much as 

 a seven-fold increase in the amount of oxygen taken up from the 

 blood. He has also shown that this increased oxygen-uptake is 

 not due to increased blood flow through the gland, for, if yohimbin 

 be injected into the arterial supply to the gland, it causes no 

 secretion of saliva and no measurable change in the oxygen used 

 by the gland, although there may be as much as a tenfold increase 

 in the blood flow through the gland. Also he has found that 

 adrenaline, which like stimulation of the sympathetic will cause 

 a secretion of saliva, causes also an increased flow of blood 

 through the gland, which begins after the commencement of 

 the flow of saliva, reaches its maximum after the salivary 

 flow has reached its maximum, and persists after the flow of 

 saliva has stopped, and long after the effect of the adrenaline 

 has disappeared from the blood pressure tracing. It causes 

 also a considerable increase in the metabolism of the gland (in 



