INTERFERENCE OF EXCITATIONS 229 



muscle under normal conditions of irritability has an inhibitory 

 effect on its antagonist. 



Finally, I wish to conclude this discussion on the origin of 

 central inhibition and its dependence upon the strength of the 

 stimulus by referring to a point which apparently is contradic- 

 tory. We have already met with the fact that series of stimuli 

 by their interference in the nervous system may have different 

 effects depending upon their intensity ; if this is strong, we obtain 

 summation of excitation, if weak an inhibition. The question 

 may be asked, how is it possible that a weak stimulus can have 

 a different effect when it is believed that the nerve as an isobolic 

 system responds to intensities of all gradations to the same extent, 

 namely, with maximum excitation? If the "all or none law" is 

 applicable, then the same intensity of excitation is always carried 

 to the centers and yet we see that various kinds of responses 

 follow various intensities of stimulation. Here, indeed, is a 

 difficulty which has not as yet been explained. Naturally between 

 the two facts there can be no contradiction. But the question 

 arises, how are we to bring them into harmony? Two entirely 

 different possibilities present themselves. If the various inten- 

 sities of stimulation always bring about excitation of the same 

 strength and we see in spite of this that various intensities of 

 stimulation produce various kinds of effects, then we must think 

 of the possibility that various intensities of stimulation bring 

 about some other effect than that of variations in intensity 

 in the course of the wave of excitation. In this connection 

 variations in the time involved must be taken into consideration. 

 One might think that strong stimuli may develop a longer wave 

 of excitation than such of weak intensity. Gotch 1 tested these 

 questions experimentally with completely negative results. A single 

 strong stimulus does not result in an excitation differing in its 

 course from that of a weak stimulus. But there is another possi- 

 bility that requires testing. This was brought to light by the 

 investigation of Thorner 2 on the fatigue of the nerve. His inves- 



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

 Journ. of Physiology, Vol. XXVIII, 1902. 



2 Thorner: "Weitere Untersuchungen iiber die Ermiidung des markhaltigen Nerven: 

 Die Ermiidung in Luft," etc. Zeitschr. f. allgem. Physiologic Bd. X, 1910. 



