324 PROTOPLASMIC ACTION AND NERVOUS ACTION 



The range of the electric variations obtained from 

 an isolated muscle which is made to contract in a graded 

 manner by single stimuli of different strengths shows 

 a direct correlation with the height of contraction, but 

 the significance of this fact is not obvious. It is pos- 

 sible (i) that the single elements or cells give action- 

 currents of varying intensity, or (2) that each element 

 has a constant variation, but that the number of 

 elements excited varies. The probabiHties favor the 

 latter alternative; in certain tissues such as heart 

 muscle, the electric variation exhibits a constant range 

 which is independent of the intensity of the stimulus; 

 the whole tissue responds with a complete contraction 

 to any sufhcient stimulus — an example of the ''all or 

 none" behavior — and correspondingly the range of the 

 electric variation is constant. There is good evidence 

 that in normal unfatigued voluntary muscle the varia- 

 tions in the strength of contraction depend on the 

 number of cells contracting, and not on variations in the 

 degree of contraction of single cells. ^ Similar considera- 

 tions apply to the bioelectric response, which in the single 

 elements of this tissue and of nerve appears also to 

 exhibit the "all or none" character. Apparently to 

 any constant manifestation of normal physiological 

 activity a constant bioelectric variation corresponds. 



On the other hand, under certain abnormal conditions 

 the bioelectric variation, e.g., in heart muscle, may 

 continue without the normally associated contraction ;'' 



^ Cf. Lucas, Journal of Physiology, XXX (1905), 125; XXXVIII 

 (1909), 113; F. H. Pratt, American Journal oj Physiology, XLIV (1917), 

 517; Pratt and Eisenberger, ibid., XLIX (1919), i. 



^Noyons, K. Akad. Wet., Amsterdam (Nov., 1908 and April, 1910) 

 (cited in Lucas' Croonian Lecture, "The Process of Excitation in Nerve 

 and Muscle," Proceedings of the Royal Society^ B, LXXXV [1912], 512). 



