ZUR LICHTREAKTION DER ISOLIERTEN FROSCHIRIS 



845 



SUMMARY 



The isolated iris of the frog ( Rana esculenta, Rana temporaria ) is capable 

 of contracting after a stimulus of light of short duration and of dilatation in the 

 dark. The amplitude and speed of contraction dépendent upon stimuli of light. 

 On the contrary the relaxion of the iris is not dépendent on stimulation. The 

 rapidity of the reaction alters with the seasons. 



Pre-illumination of long duration, modifications of the ionic milieu and 

 catecholamines reduce the amplitude and the speed of light-induced contraction. 

 Différent drugs and réduction of termperature have no efTect on the amplitude. 

 The speed of contraction is slowed by réduction of température and pre- 

 illumination of long duration but is not influenced by modification of the ionic 

 milieu. 



The effects of the catecholamines take place by means of the /?-receptors. 

 The irides of reserpine-treated frogs react similary to untreated animais. The \ 

 accélération of the speed of contraction by réduction of température is anta- 

 gonised by Isoproterenol. 



The receptors of the végétative System of the frog-iris resemble those of 

 highly evolved vertebrates. 



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