ABSTRACT
The rhythmical stimulation of heart muscle, according to the myogenic theory, is of the nature of an auto-stimulation, dependent upon certain processes in the muscle cells themselves. These processes are associated with a system in the cell which undergoes a rapid alteration when a certain critical condition is reached, with a stimulation of the cell resulting. The system then gradually reconstructs itself, undergoing a similar breakdown when the “critical condition” is reached a second time. The time required for the system to pass from the condition existing at stimulation till the critical condition is again attained determines the rate of beat of the heart muscle cell. This unstable system is closely associated with the entire responsive mechanism in the cell and, therefore, is susceptible to modification by the same conditions which are known to modify other phases of the response of the cardiac muscle, such as the duration and magnitude of contraction. The analysis of the exact nature of the relation existing between the rhythmic process and other processes inherent in the system, under conditions known to modify all cellular processes, is essential to any elucidation of the mechanism. The present paper presents the results of an investigation of the action of temperature upon the automatic rate of the sinus and the duration of the simple sinus twitch.
Results somewhat similar to the above have been obtained by Clark (1920) for the ventricle Of the frog.
The exact nature of the intracellular changes, produced by the repeated stimulation, which serve to modify the contractile process, are not known, but most probably are associated with an alteration in the total energy transformation in the response rather than any change in the efficiency of the process.
