THE VISUAL PIGMENTS 



Another generalization can be made with the help of Houstoun's 

 equations which we ale (1949a, b) used for calculating molecular 

 weights (Chap. 3, p. 92). Houstoun related the molecular extinction 

 coefficient at the Amax (cmax) with the shape of the density spectrum 

 by the following equation, 



. . •^ max 



^max 



A.P 



rX 



jmax 



i-max 



Where ^ is a constant and the other symbols are defined on p. 92 of 

 Chap. 3. The term A^max in this equation is an approximation for 



-^max-^imax. Now, 



^jmax — M 



^imax^max 



— '^max — '^imax 



Thus the £max is inversely proportional to the width (in frequency 

 units) of the band at its semi-maximal height. Since the absorption 

 bands of the visual pigments are approximately the same shape, this 

 leads to the result that £max, the molecular extinction coefficients of 

 the visual pigments, should have approximately the same value at 

 their respective maxima. 



DISCUSSION 



So far, retinal extracts from five fish have been examined by the 

 partial bleaching technique. The results obtained are tabulated 

 below. 



* Pigments 510 (bleak) and 507 (rainbow trout) have been assumed to be the same. 



In the table, the figures represent the average proportions of the 

 pigments present. Thus '100* indicates that only one pigment was 

 found. The other figures compare the densities of the pigments at 



17§ 



