COLOURING MATTER OF SULPHUR BACTERIA 241 



From equations (i) and (2) we get 



Hence 



I2 (Di)^- 

 •I'-i- ^ 



(3) 



Or the fraction of the Hght absorbed by the coloured fluid 

 is thus 



Thus the effect of the insertion of the coloured fluid on the 

 intensity of the light can be accurately calculated for each 

 part of the spectrum. 



Results with Thioporphyra volutans. 



Confirmation was obtained of the absence of definite 

 absorption bands and localized darkened areas in the ab- 

 sorption spectra of this organism. 



Summary. 



The colouring matter of Thioporphyra volutans is similar 

 to that of other sulphur bacteria in being composed of two 

 groups of substances, one of which forms a purple colour 

 in some solvents, e.g. chloroform, whilst the other forms a 

 brownish-green colour in other solvents, as e.g. ether. The 

 former does not appear to be identical with the phycoerythrin 

 of the Floridese (Fig. 65, X), nor does the latter show any 

 relationship with chlorophyll. Spectroscopic analysis show 

 the absence of absorption bands and of localized darkened 

 areas in cultures on cardboard, but these were found in 

 cultures on Fucus. The want of stabihty of such bands and 

 areas in the absorption spectra makes this method of inves- 

 tigation very uncertain. At present it is not possible to 

 associate the colouring matter of Thioporphyra volutans with 

 any arrangement of dark bands in its absorption spectrum. 



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