INHIBITION AND CARDIAC VAGUS 115 



and keep on repeating, that a normal stimulus can have a 

 direct weakening effect does not convince those desirous 

 of examining the problem afresh. It may be recalled, 

 perhaps, not without advantage, that many single experi- 

 ments, or even dicta of authoritative ancient physicians, 

 are as duly repeated from one text-book to another as 

 wrong definitions in some big dictionary are copied in its 

 successors. In any case the physiologists and pharma- 

 cologists speak not as physicians, most of whom, I imagine, 

 are under the impression that digitalis in therapeutic doses 

 aids vagus action, slows the pulse, obtains a better diastole 

 directly, and allows the heart pause sufficient time to gather 

 up its energy and increase its general tone and its haemic 

 output with relief to all the symptoms which called for its 

 assistance. When the heart has been thus helped the 

 accelerator is no longer irritated into increasing the heart- 

 rate, the pace-maker is restored to its normal action, 

 and once more dominates the irregular discharges of the 

 degenerate myocardium. To say, as the students of drugs 

 say, that the symptoms in the second, or poisonous, stage 

 of digitalis are like vagus action, and that cardiac work is 

 therefore less well done, is to mix true observations with 

 false. At the least it seems to imply that digitalis then 

 acts through and on the vagus nerve, whereas its thera- 

 peutic action suggests that what it does is to increase the 

 working capacity of the cardiac muscle by modifying its 

 irritability and allowing it time to recuperate, thereby 

 permitting normal vagus action to continue. It thus 

 assists the complex reversible reactions which enable 

 muscle to work at all. If larger doses stop action directly, 

 or prevent the muscle cells from being supplied with 

 necessary proteins, or with fuel, it is in such cases that the 

 word "inhibition" seems truly applicable, for poisonous 



