18 



Professor J. A. MacWilliam. 



Any influence which depresses excitability without depressing — at least 



proportionately — the function of conduction naturally tends to be in some 



measure protective against the occurrence of fibrillation and favourable to 



recovery from that condition when once it has been estabhshed. A diminution 



of excitability opposes the attainment of acceleration sufficient to determine 



fibrillation ; it also diminishes the responsiveness of the muscular fasciculi to 



circulating excitations. (The control of auricular fibrillation which differs in 



some respects from that of ventricular fibrillation will be dealt with elsewhere.) 



Similarly any agency which improves conductivity without unduly exalting 



excitability is inimical to the mechanism of circulating excitation. Obviously 



a combination of a depressing influence on excitability with the maintenance 



of a high level of conductivity would afford the most favourable condition for 



protection or recovery. Concurrent depressions or elevations of excitability 



and conductivity in proportionate degree naturally have no specific influence 



on the question of fibrillation. The agencies which operate successfully in 



opposing the development of fibrillation — either spontaneous {i.e. from 



unknown causes) or excited artificially by drugs, electrical stimulation, etc. — 



are often effective in restoring the normal action after fibrillation has been 



established. Eemedies for fibrillation have commonly, in these experiments, 



been injected into the cavity of the left ventricle through the apex by means 



of a slender needle ; sometimes intravenous injection (external jugular, etc.) 



was used, massage of the heart being done in both cases, while the artificial 



respiration is of course maintained. Smaller doses were sufficient by the 



intra-ventricular mode of injection. Approximately isotonic solutions were 



used, warmed to body temperature. The doses stated are for cats, usually 



weighing 2-3 kilos, but sometimes more. 



Urethane. — Doses varying between 0'025 and 0*25 grm. injected into the 

 left ventricle were found effective in removing fibrillation in very numerous 

 experiments (fig. 10); 3 per cent, solutions were commonly used for 



Fia. 10. — The middle portion of the tracing shows fibrillation caused by strong 

 faradisation (5000 units). After it had lasted for 2 minutes (with occasional 

 massage) 0'05 grm. urethane was injected into the L.V. The restored action is seen 

 in the right-hand portion. 



( 319 ) 



