642 INTERNAL SECRETION 



maintenance of the normal vaso-motor tone, and therefore to the 

 maintenance of the normal blood-pressure. All the best evidence 

 is against this view. Whatever influence the relatively small 

 quantities of adrenalin discharged from time to time may have upon 

 the nutrition of the smooth or of other muscles, it is quite unlikely 

 that such amounts are continuously entering the blood as injection 

 experiments have shown to be necessary for the maintenance of even 

 a small excess of blood-pressure. Statements which connect the 

 increased blood-pressure in such conditions as chronic nephritis with 

 hypertrophy of the chromamn tissue (p. 643), an increased adrenalin 

 production, and an increased adrenalin content of the blood, must 

 be received with scepticism. The so-called experimental arterio- 

 sclerosis produced by repeated injections of adrenalin into the 

 blood of rabbits throws little light upon the question, for the 

 vascular changes, in so far as they have not been confounded with 

 similar lesions occurring spontaneously in a considerable proportion 

 of rabbits, differ from those observed in pathological arterio- 

 sclerosis (M. C. Hill). 



Certain facts indicate, indeed, that doses of adrenalin considerably 

 smaller than those which give the effects described above, and 

 usually considered the ' normal ' effects, produce a reversal of the 

 reaction, very small doses causing, for instance, a diminution of 

 blood-pressure (Moore and Purington), an increase in intestinal 

 tonus and peristalsis, and a diminution in the tone of uterine seg- 

 ments. The actions associated with these small doses are more 

 likely to be the normal actions than those associated with the 

 larger doses, and the normal action of adrenalin, if it is a continuous 

 action, would therefore more probably be to inhibit than to excite 

 the sympathetic mechanism. But there is no evidence that even 

 quantities of this order of magnitude are continuously discharged. 

 The continuous introduction of epinephrin at a very slow rate 

 produces no demonstrable effect at all, and the sudden ligation of 

 all the adrenal bloodvessels has not the slightest influence upon 

 the blood-pressure until the lapse of a period far greater than would 

 be required for the destruction or removal a quite rapid process 

 of any epinephrin already present in the blood or tissues (Tren- 

 delenburg, Hoskins). The injection of a quantity of adrenalin 

 sufficient to cause and to long sustain even a minimal increase of 

 blood-pressure creates conditions highly hazardous to life or in- 

 compatible with it namely, complete paralysis of the gastro- 

 intestinal tract. 



The suggestion that enough epinephrin may be continuously 

 liberated to exert an influence upon the nutrition and metabolism 

 of the sympathetic system, or of the myoneural junction, which is 

 necessary for normal excitability, without ever rising to the thres- 

 hold of actual excitation, is a mere hypothesis, and a hypothesis 



