1184 PHYSIOLOGY 



but in every case is identical with that obtained by stimulting the hypogastric 

 nerves. It has been shown by Dale that adrenaline may also excite vaso- 

 dilator fibres or produce vaso- dilator effects when such effects are also 

 obtained from stimulation of the sympathetic nerves. In order to evoke 

 these results it is necessary to paralyse the vaso- constrictors by the injection 

 of ergotoxin, one of the active principles of ergot. This drug, when injected, 

 causes first active vaso- constriction and rise of blood-pressure, followed by 

 paralysis of the vaso- constrictor mechanism. Excitation of the splanchnic 

 nerves or injection of adrenaline will now bring about a fall of blood-pressure 

 due to dilatation of the vessels in the splanchnic area. 



The point of attack of the adrenaline appears to be in the muscular or 

 glandular tissues themselves, since it may be obtained not only after destruc- 

 tion of the cord and sympathetic plexuses but even after time has been 

 allowed for the peripheral (post-ganglionic) fibres to degenerate as a result of 

 extirpation of the corresponding ganglia. Although the effect is not altered 

 under these circumstances, and it may still produce either relaxation or 

 contraction of muscles according to the original action of the sympathetic 

 on these fibres, we are not justified in regarding it as acting on the contractile 

 material of the cells themselves. Rather must we assume with Langley and 

 Elliott that the action of adrenaline is on some substance mediating between 

 the nerve and the responsive tissue. We may speak of this reactive material 

 as the receptor substance (Langley), or we may locate it in the situation 

 where the nerve joins the muscle or gland- cell and describe adrenaline as 

 acting on the myoneural junction. 



Each suprarenal receives a number of filaments from the splanchnic 

 nerve on its own side. These pass to the medulla where they end apparently 

 without the interposition of any ganglion cells on their course (Elliott), the 

 cells of the medulla having themselves been developed by a modification of 

 sympathetic ganglion cells. Stimulation of the peripheral end of the 

 splanchnic nerve causes, as we have already seen, a discharge of adrenaline 

 into the blood-stream. This discharge accounts for the secondary rise, 

 often accompanied with quickening of the heart, observed on a blood- 

 pressure tracing as the result of stimulating the splanchnic nerve. Through 

 the splanchnic nerves a discharge of adrenaline can be excited by many 

 general conditions, such as pressure on the brain, puncture of the fourth 

 ventricle, administration of anaesthetics, mental conditions such as excite- 

 ment or fright. Such a discharge is an important element in the reaction to 

 environmental stress and enables the animal to react for the preservation of 

 its life either by offence or flight. If one splanchnic nerve be cut before the 

 administration of anaesthetics or the maintenance of a condition of irritation 

 or fright, the suprarenal gland on the corresponding side will be found to 

 contain two or three times as much adrenaline as the gland which has been 

 left in connection with the central nervous system. It is interesting that 

 no such condition of exhaustion can be produced by electrical stimulation of 

 the peripheral end of the divided splanchnic. It has been suggested, 

 therefore, that the splanchnic nerve contains two sets of fibres, anabolic 



