SELIG HECHT 389 



The results with spectral Kghts therefore sum up to this. With 

 Mya the effectiveness of the spectrum depends exclusively on the ab- 

 sorption spectrum of the photosensitive substance in the sense organ. 

 The different positions of the maximum effectiveness for various 

 organisms merely show that the sensitive substances concerned are 

 different entities, each possessing its own absorption spectrum. 



SUMMARY. 



1. Following the description of a simple method of securing high 

 intensities of monochromatic illumination, it is shown that the most 

 effective portion of the spectrum for the stimulation of Mya is near 

 X = 500 fXfjL. 



2. The quantitative data secured is interpreted in terms of certain 

 photochemical findings, and as a result the absorption spectrum of the 

 photosensitive substance of Mya is tentatively mapped out. 



Through the courtesy of Doctor M. Luckiesch of the Nela Research 

 Laboratory, Mr. W. E. Forsythe and Mr. F. E. Cady determined the 

 energy distribution for the 400 watt lamp which I used in these experi- 

 ments. I take pleasure in thanking them for their help in this 

 connection. 



BIBLIOGRAPHY. 



Bovie, W. T., An approximation of the value of the absorption index of fluorite 

 rays in protoplasm, /. Med. Research, 1918-19, xxxix, 239. 



Brooks, S. C, Precise titration of complement, /. Med. Research, 1920, xli, 399. 



Hecht, S., (a) Sensory equilibrium and dark adaptation in Mya arenaria, J. Gen. 

 Physiol., 1918-19, i, 545; {b) The nature of the latent period in the 

 photic response of Mya arenaria, 657; (c) The effect of temperature on 

 the latent period in the photic response of Mya arenaria, 667; {d) Intensity 

 and the process of photoreception, 1919-20, ii, 337; (e) Time and intensity 

 in photosensory stimulation, 1920-21, iii, 367. 



Henri, V., fitudes de Photochimie, Paris, 1919. 



Hess, C, Neue Untersuchungen liber den Lichtsinn bei wirbellosen Tieren, Arch, 

 ges. Physiol., 1910, cxxxvi, 282. 



Lasareff, P., tjber das Ausbleichen von Farbstoffen im sichtbaren Spektrum, Ann. 

 Physik, 1907, xxiv, 661. 



Laurens, H., and Hooker, H. D., Jr., Studies on the relative physiological value of 

 spectral lights. IL The sensibility of Volvox to wave-lengths of equal energy 

 content, /. Exp. ZooL, 1920, xxx, 345. 



