322 Mechanism and Control of Fibrillation in Mammalian Heart. 



kilogi'amine ut' body-weight showed striking effects in opposing the develop- 

 ment of fibrillation, either " spontaneously " or in response to electrical 

 stimulation, etc. Even powerful faradisation (often several thousand units) 

 caused only a pseudo-fibrillation, ceasing almost immediately or lasting only 

 a short time (seconds) after the stoppage of the current, or a true fibrillation, 

 which is spontaneously recovered from — on account of the diminished 

 responsiveness of the muscle to the circulating excitations. 



Pilocarpine. — Intravenous injection (into jugular, etc.) of 0'0025 grm. (with 

 massage of the ventricles) was often effective in arresting ventricular 

 fibrillation. There was a good deal of variation in regard to this result ; 

 there seemed to be a parallelism between the efficiency of pilocarpine in 

 this respect and the activity of vagus inhibition in the particular heart in 

 question — as tested by stimulation of the vagus in the neck or, preferably, 

 the inhibitory area on the dorsal- aspect of the auricles. Though vagus 

 stimulation has not been found to arrest fibrillation once it has been 

 established, it has shown notable effects in opposing the development of 

 fibrillation in certain circumstances. And pilocarpine is much more potent 

 than the vagus, though its influence is in the same direction and of the same 

 nature in many respects at least. 



Similar remedies were found applicable to the perfused heart, also, a 

 little of the solution of urethane, adrenalin, etc., being injected into the 

 tube leading to the aorta ; very small doses usually sufficed. 



In some instances, where ventricular fibrillation does not yield so readily 

 as usual to a single remedy, combinations such as urethane and adrenalin, 

 or these followed by strontium chloride, prove very effective. After such 

 treatment the ventricles commonly show a remarkably great resistance 

 to electrical stimulation as far as the induction of fibrillation is concerned, 

 very powerful currents up to 7,000-10,000 units, etc., often causing only 

 pseudo-fibrillation, and, if true fibrillation, with its special mechanism, is 

 induced, it very frequently shows spontaneous recovery after variable 

 periods, frequently without any massage or with massage for some seconds. 

 The difficulty in exciting fibrillation, and its notable tendency to recover, 

 are often very striking, and are to be accounted for, in the main at least, by 

 the diminished responsiveness of the muscle induced by the drugs. 



Some relations of different remedial agents to special conditions of the 

 heart may be noted. In very excitable hearts that have fibrillated, 

 depression of excitability is the primary requirement. On the other hand, 

 when direct depression of conductivity {e.g., by potassium salts, bile, cooling, 

 etc.) is the predominant factor in any particular heart, remedies calculated to 

 enhance this function are obviously indicated, whether they act (a) by 



