1046 PHYSIOLOGY 



ACTION OF ADRENALINE. This substance, produced by the supra- 

 renal glands, has a marked influence on the calibre of the blood vessels. 

 If 1 c.c. of a 1 in 10,000 solution of this substance be injected into the jugular 

 vein, there is at once a universal constriction of the arterioles with the 

 exception of those of the brain. If the vagi are cut, we obtain a simultaneous 

 augmentor action of this drug on the heart and constrictor effect on the 

 blood vessels, so that the arterial pressure rises to an enormous extent, up 

 to 300 mm. Hg. or more. The same result occurs after section of the vaso- 



FIQ. 479. Curve showing the effect of a sudden rise in the arterial resistance on 

 the output and volume of the ventricles. Systole causes a downward movement 

 of the lever. 



H, heart volume ; BP, arterial blood pressure ; s, signal showing duration of 

 stimulation of splanchnic nerve ; T, time marker, 10 sees. 



motor nerves or after destruction of the brain and spinal cord, so that there 

 is no doubt that adrenaline acts directly on the blood-vessel wall. The 

 action of this drug as a whole is therefore largely to augment the energy of 

 the circulation. The arterial pressure rises, and the blood will be therefore 

 travelling at a much greater pace through any part, of the body where the 

 vessels are maintained in a dilated condition, e. g. in an active muscle, or 

 where there are no vaso-motor nerves, as in the vessels of the brain. It is 

 therefore not surprising that we have evidence of the secretion of adrenaline 

 in increased quantities into the blood during any condition of stress. When- 

 ever the splanchnic nerve is stimulated, there is an increased production of 

 adrenaline. On this account the rise of pressure produced under these 

 circumstances shows a stepped curve, the first rise being due to the direct 

 action of the vaso-motor nerves of the blood vessels, the second being 



