Control of Fih7'illation in the Mammalian Heart. 321 



chloroform -adrenalin reaction described by Levy and abundantly illustrated 

 in this investigation), intravenous injection of potassium salts, etc. In many 

 instances fibrillation has been induced by a small dose (e.g., 01 mgrm.) of 

 adrenalin and remedied by the intraventricular injection of a very large dose 

 (up to 1 mgrm.), the state of the heart and circulation remaining good after- 

 wards (fig. 12). The excitability and conductivity of the muscle are 



A. B. C. 



Fig. 12. — The uppei- tracing is from the left ventricle, the lower indicates the blood- 

 pressui'e. In A, fibrillation caused by faradisation with 1500 units lasted 6 minutes, 

 recovery following injection of 5 mgrm. adi'enalin in three doses. B is shortly 

 after recovery. C, taken 1 minute later, shows much increase in the range of the 

 lever excursions. Note that the blood-pressure is still elevated. 



enhanced by a small injection and as early effects of a large injection ; 



subsequently a pronounced depression of excitability occurs — shown in 



many cases by a great diminution in responsiveness when tested by graduated 



faradic currents ; stimulation, that formerly induced fibrillation readily, now 



fails to do so even when strengthened to many times its former intensity. 



Diminished sensitiveness to faradic currents is often pronounced, while the 



blood-pressure is still elevated and the heart is beating very strongly. 



Adrenalin can thus act in two ways : (a) by reducing excitability, and (b) by 



improving conduction. 



Hinulin. — Injections* (into the saphenous vein) of about 8-10 mgi-m. per 



* Doses of 0"3-0"5 mgrm. were often effective in removing fibrillation injected into the 

 L.V. The solution of hirudin used generally contained 1 mgrm. in each cubic 

 centimetre of Ringer's fluid. 



