50 IRRITABILITY 



by direct stimulation of a bundle of curarized muscle fibers, 

 the contraction only increases inconstantly and not regularly 

 with the increasing intensity of the stimulus. This is only 

 comprehensible if one takes into consideration that, with the 

 increasing intensity of the stimulus, a greater and greater number 

 of fibers are stimulated. Keith Lucas'' came to the same con- 

 clusion in the case of the muscle stimulated indirectly through 

 the nerve. He, therefore, sees, because of the nature of the 

 response of the single muscle cell, no difference between heart 

 muscle and skeletal muscle. The "a// or none law" applies to the 

 individual muscle cells of both kinds. The difference between 

 the heart and skeletal muscle, according to him, lies in the fact 

 that in the heart the individual muscle cells in their totality stand 

 together as conductors of excitation, whereas in the skeletal 

 muscle the individual muscle fibers are separated, as far as con- 

 duction of excitation is concerned, by the sarcolemma. Finally, 

 the recent investigations of Vessi^ with strychnine poisoned gan- 

 glia cells of the posterior horns of the spinal cord, have made it 

 appear probable that "the all or none law" can be applied like- 

 wise to the individual ganglion cell. He draws this conclusion 

 not only from the fact that all reflex contractions of a muscle 

 of a strychninized frog are maximal, whether they are produced 

 by weak or strong stimuli, but also especially because of the 

 loss in the strychninized spinal cord of the capacity of the summa- 

 tion of irritability. The normal spinal cord does not reflexly 

 respond at all to weak single stimuli, but responds to equally 

 weak faradic stimulation very readily. Therefore, the threshold 

 lies very high for the individual induction shock and very low 

 for faradic shocks. But these differences are equalized in the 

 strychninized frog. This seems intelligible, when we assume 

 that the strychninized cell responds to every stimulus, to which 

 it responds at all, to the maximal extent which is permitted at 

 that moment by its stored up energy, otherwise the excitation 

 would necessarily be summated by faradic stimulation. 



1 Keith Lucas: "The all or none contraction of skeletal muscle fibre." Journal of 

 Physiology, Vol. XXXVIII, 1909. 



2Vcsz\: "Zur Frage des Alles oder Nichts-Gesetzes beim Strychninfrosch." Zeit- 

 schrift fiir allgemeine Physiologie Bd. XII, 1911. 



