66< INTERNAL SECRETION ENDOCRINE GLANDS 



The function of the spontaneously liberated epinephrin, once it 

 has entered the circulation, is accordingly involved in doubt. The 

 common view that it exerts an important physiological action upon 

 the sympathetic system, contributing especially to the maintenance 

 of the normal blood-pressure is opposed to all the best evidence. 

 \Yhatever influence the relatively small quantities of adrenalin dis- 

 charged 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 chromafrin tissue (p. 665), an increased adrenalin production, 

 and an increased adrenalin content of the blood, must be received 

 with scepticism. The so-called experimental arteriosclerosis pro- 

 duced by repeated injections of adrenalin into the blood of rabbits 

 throws little light upon the question, for the vascular changes, in 

 so far as the}' have not been confounded with similar lesions occur- 

 ring spontaneously in a considerable proportion of rabbits, differ 

 from those observed in pathological arteriosclerosis (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 inhibition of the muscula- 

 ture of the gastro-intestinal tract. 



The only effect of interference with the passage into the blood of 

 the spontaneously liberated epinephrin which has hitherto been demon- 

 strated is upon a mechanism rendered abnormally sensitive namely, 



