1324 PHYSIOLOGY 



obtained by stimulating the hypogastric nerves. It has been shown 

 by Dale that adrenalin may also excite vaso-dilator fibres or produce 

 vaso-dilator effects when such effects are also obtained from stimula- 

 tion of the sympathetic nerves. In order to evoke these results it is 

 necessary to paralyse the vaso-constrictors by the injection of ergo- 

 toxin, 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 adrenalin 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 adrenalin appears to be in the muscular 

 or glandular tissues themselves, since it may be obtained not only 

 after destruction 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. Kather must we assume with Langley and Elliott that 

 the action of adrenalin 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 adrenalin as acting on the myoneural junction. Schafer also 

 mentioned the influence of adrenalin on voluntary muscle, but later 

 observers have failed to substantiate any marked specific influence on 

 this tissue. 



When adrenalin is injected into the blood-stream the effect is 

 only temporary. It is not excreted in the urine, but rapidly dis- 

 appears from the blood. Since it is easily oxidised and is extremely 

 unstable in alkaline solution, we may conclude that after performing 

 its excitatory function it is destroyed by oxidation in the fluids. 

 Adrenalin is thus a typical hormone, a body of comparatively low 

 molecular weight, having a drug-like excitatory action on specific 

 tissues of the body, easily diffusible, and rapidly destroyed after dis- 

 charging its office. Owing to the rapid destruction of adrenalin, 

 relatively enormous doses have to be given by the mouth in order to 

 produce any effect on the blood pressure. There is, however, a whole 

 series of substances, more or less allied to adrenalin in chemical con- 

 stitution, which undergo less rapid destruction and can therefore be 

 administered as drugs in the usual way. Dale and Barger have 

 recently described three such substances as occurring in infusions 

 of putrid meat and as forming the most important of the active 



