THE CHARACTERISTICS OF STIMULI 49 



considerably in different living substances. In this connection 

 there are several forms of living substance which call for our 

 special attention. In these the surprising condition seems to exist, 

 that the interval between the threshold and the maximal stimulus 

 is zero; that is, every stimulus which acts at all always produces 

 a maximal response. Bowditch^ first observed this behavior in 

 the frog's heart and this has also been confirmed by Kronecker.^ 

 The induction current produces, as Bowditch says, either a con- 

 traction or nothing. If the former, it is the strongest contrac- 

 tion which can be produced by an induction shock at the given 

 time. Here for the first time a constancy of response was dis- 

 covered which has been termed the all or none law. McWilliams^ 

 has later verified the same fact for the mammalian heart. 

 Gotch* has also arrived at the same conclusion in connection with 

 the nerve. He states that "the comparisoa of submaximal with 

 maximal responses shows that although there is an obvious difiier- 

 ence in the amount of E. M. F., there is little or no difference 

 between such time relations as the moment of commencement, the 

 moment of culmination of E. M. F. and the rate at which E. M. F. 

 disappears." Further : "the rate of propagation of the excitatory 

 wave is the same whether this is maximal or submaximal." He 

 likewise assumes that the "all or none law" is applicable to the 

 constituent fibers, and that the variations in the strength of 

 response with weak and strong stimulation are brought about 

 in the first instance by stimulation of a few, in the latter by 

 a greater number of fibers in the nerve trunk. The same con- 

 clusion has been reached by Keith Lncas^ for the single cross- 

 striated fiber of the skeletal muscle, founded on the fact that 



1 Bowditch: "XJeher die Eigentumlichkeiten der Reizbarkeit, welche die Muskel- 

 fasern des Herzens zeigen." In Arbeiten aus der physiologischen Anstalt zu Leipzig 

 VI. Jahrgang 1872. 



2 Kronecker: "Das characteristische Merkmal der Herzmuskelbewegung." In 

 Beitriige zur Anat. und Physiol. Als. Festgabe Carl Ludwig gewidmet von seinen 

 Schiilern. Leipzig 1874. 



3 McWilliams: "On the rhythm of the mammalian heart." Journal of Physiology, 

 Vol. IX, 1888. 



AGotch: "The submaximal electrical response of nerve to a single stimulus." 

 Journal of Physiology, Vol. XXVIII, 1902. 



5 Keith Lucas: "On the graduation of activity in a skeletal muscle fibre." Journal 

 of Physiology, Vol. XXXIII, 1905-06. 



