THE REFRACTORY PERIOD AND FATIGUE 157 



artificial systole can only be produced with certainty when the 

 stimuli succeed each other at certain intervals, which must be the 

 longer as the strength of the stimulation is weaker. Marey calls 

 this period of reduced irritability "phase refractaire'' of the heart. 

 The refractory period of the heart has been made the subject of 

 a great number of investigations, especially by Engelmann and 

 his pupils. It was Engelmann 1 especially who determined more 

 exactly the duration of the course of the refractory period. He 

 found, namely, that irritability disappears immediately before 

 each systole and reappears shortly before the beginning of the 

 diastole, and again reaches its original height at the end of the 

 diastole. For a long time, however, this refractory period was 

 looked upon as a special peculiarity of the heart. It was not until 

 Broca and Richet, 2 twenty years after Marey's investigations, dis- 

 covered an analogous refractory period for the motor centers of 

 the cerebral cortex of the dog. They first made this observation 

 on a dog affected with chorea, in which the choreic movements 

 rhythmically occurred in intervals of one second. They found that 

 after each movement electrical stimulation of the cortex remained 

 without result for about .5 seconds. During the next .25 seconds 

 stimulation was followed by a weak response and it was not until 

 the last .25 seconds before the next movement that a strong 

 effect was produced. They also found in the normal dog a re- 

 fractory period after every artificial stimulation equal to .1 

 second, so that the number of contractions brought about by 

 rhythmical electrical stimulation were only ten per second. Follow- 

 ing this, numerous other investigations of the refractory period 

 have been made on the central nervous system. Zwaardemaker 3 

 and Lans have observed a refractory period in the eyelid reflex 

 of the human being which, on stimulation of the optic nerve, 



1 Th. W . Engelmann : "Beobachtungen und Versuche am suspendierten Herzen 

 III. Refractare Phase und compensatorische Ruhe in ihrer Bedeutung fur den Herz- 

 rhythmus." Pfliigers Arch. Bd. 59, 1895. 



2 Broca et Richet: "Periode refractaire dans les centres nerveux." Comptes rendus 

 de 1'academie des sciences 1897. Further Richet: "La vibration nerveuse." Revue 

 scientific Dec. 1899. 



3 Zwaardemaker und Lans: "Ueber das Stadium relativer Unerregbarkeit als 

 Ursache des intermittierenden Charakters des Lidschlagreflexes." Centralblatt fur 

 Physiol. XIII, 1899. 



