COLOURING MATTER OF SULPHUR BACTERL4 233 



discovery that certain purple bacteria, particularly Bacterium 

 photometriciim, when exposed to light congregated more densely 

 at tliat part of the spectrum where the absorption of light was 

 greatest (see Chap. XI). He recorded two absorption bands : — - 



I. 61A — 57A (orange to green) ; sharply defined) . 



2- 55A— 52A (green) ; less well defined J &• 5, 



A darkening was observed in the violet end, beginning near 

 50A, and a slight darkening in certain other parts of the 

 spectrum. The maximum light intensity lay in the red at 

 62A — 63A. It is thus seen that this pigment differs spectro- 

 scopically from the chlorophylls and the carotinoids of higher 

 plants. 



Biitschli first observed that there were two pigments, 

 one soluble in alcohol, and the other only slightly so. The 

 former, which imparted a purple colour to the alcohol, formed 

 crystals which turned blue with sulphuric acid, and blue-green 

 with iodine. This occurs also with the colouring matter of 

 Eugenia sanguinea. He therefore regarded the colouring 

 matter of both of these organisms as being a form of carotin. 



Arzichowsky claimed to have discovered two red colouring 

 matters, which he named hacieriopiirpurin and bacterio- 

 erythrin respectively. Unfortunately the first of these names had 

 been used in a different sense by Ray Lankester. His claim for 

 the presence of two colours rested on the fact that a wet 

 filter-paper dipped in the purple extract first took up a rose- 

 red colour, which was a different tint from that left behind. 

 Further, the separation could be eft'ected by shaking the 

 extract with carbon bisulphide when the bacterioerythrin 

 separates from the alcohol, imparting a raspberry colour to 

 the solvent. Molisch (3) experimented with pure cultures 

 of Rhodobacilliis palustris. He also found two colouring 

 matters : — 



1. A green colour which he named bacteriochlorin. 



2. A red colour which he named bacteriopurpitrin. 



The name bacteriopurpitrin is used here by Molisch with 

 still another meaning. 



Bacteriochlorin is soluble in benzene, olive oil, turpentine 

 oil, and chloroform. 



