SELIG HECHT 13 



assuming that X is a substance whose concentration in the system is 

 so great that it suffers no sensible change during the reaction. Further 

 discussion of these matters will, however, be postponed to a time when 

 more data will have been presented. 



SUMMARY. 



1. Visual purple solutions are prepared under such conditions that 

 the bleaching reaction is irreversible. 



2. A method is described for the colorimetric estimation of very 

 small quantities of visual purple. By this means the kinetics of the 

 bleaching reaction are investigated. 



3. The results show that the course of the decomposition follows 

 that of a monomolecular reaction, without any measurable period 

 of induction or after effect. 



BIBLIOGRAPHY. 



Boll, F., Zur Anatomic und Physiologic der Retina., Monatsber. Berlin. Akad., 

 1876, 783. 



Ewald, A., and Kiihne, W., Untersuchungcn iiber den Schpurpur, Unters. physiol. 

 Inst. Heidelberg, 1878, i, 139. 



Hccht, S., The dark adaptation of the human eye, /. Gen. Physiol., 1919-20, ii, 

 499. 



Lewis, W. C. McC, A system of physical chemistry, New York, Bombay, Cal- 

 cutta, and Madras, 1918, i. 



Parker, G. H., and Patten, B. M., The physiological efifect of intermittent and of 

 continuous lights of equal intensities, Am. J. Physiol., 1912-13, xxxi, 22. 



Sheppard, S. E., Photochemistry, New York, 1914. 



Trendelenburg, W., Quantitative Untersuchungen iiber die Bleichung des Seh- 

 purpurs in monochromatischem Licht, Z. Psychol, u. Physiol. Sinnesorg., 1904, 

 xxxvii, 1; Die objectiv feststellbaren Lichtwirkungen an der Netzhaut, 

 Ergebn. Physiol., 1911, xi, 1. 



