166 IRRITABILITY 



with two stimuli in quick succession and used the contractions 

 of the triceps as indicator of the response. He found that when 

 the stimuH, if consisting in either single induction shocks or 

 faradic shocks, followed each other even at intervals of .004 

 seconds the second stimulus was still operative, this being per- 

 ceptible in an increase of the contraction or with greater inter- 

 vals of time in a summation of two contractions. IVintersfein 

 concludes from this that the development of a refractory period 

 after a stimulation is not a general property of all nerve centers. 

 If the experiments of Langcndorff failed to show the presence 

 of a refractory period it is not for the reason that this does not 

 take place in the centers of the spinal cord but rather results from 

 the fact that the conditions for the investigation were not suited 

 for its demonstration. In fact, Frolilich^ and especially VessP 

 have incontestably proved the existence of relative refractory 

 periods in the normal spinal cord. 



If the existence of the refractory period is based on the fact 

 that during the time of and subsequent to an excitation the quan- 

 tity of substances necessary for disintegration is decreased and 

 that of the breaking down products increased, and if it is limited 

 by the restitution of the substances required for decomposition 

 and the elimination of the disintegration products, its duration 

 must be dependent upon the length of these processes. All fac- 

 tors which lessen the decomposition and hasten the metabolic 

 self-regulation must, therefore, shorten its duration. This is 

 completely confirmed by experimental investigations. As can be 

 understood, the factors of special interest for us are those which 

 influence the duration of the refractory period in the physiologi- 

 cal occurrences of the organism. 



One of these factors is temperature. As we know, the rapidity 

 of chemical reactions increases with ascending and decreases with 

 falling temperature. As in the disintegration as well as in the 

 restitution, processes are chemical in nature, it is to be expected 



1 Fr. W. Frohlich : "Beitrage zur Analyse der Reflexfunction des Ruckenmarks 

 mit besonderer Beriicksichtigung von Tonus, Bahnung und Hemmung." Zeitschrift f. 

 allgem. Physiologie Bd. IX, 1909. 



2 Julius Vessi: "Der einfachste Reflexbogen im Ruckenmark." Zeitschr. f. allgem. 

 Physiologie Bd. XI, 1910. 



