ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 395 



It occurs to such au extent as often to almost obliterate the 

 F band; thus this band is figured as absent in Dr. Benham's 

 maps, though Dr. Engelmann's chart indicates its presence. 



By neutralisation with alkali the orij^inal spectrum and 

 colour may be restored — a marked difference from the pheno- 

 mena exhibited by solutions of chlorophyll. 



(2) Action of Acids on Chajtopteriu. 



The changes which solutions of cheetopterin undergo on the 

 addition of acids are of so striking a nature that they form a 

 natural starting-point for any investigation. 



The acid usually employed was hydrochloric acid in con- 

 centrated solution. The employment of gaseous hydrochloric 

 acid produced the same effect as the solution ; it did not 

 produce a precipitate, as it does in the case of solutions of 

 chlorophyll. It was found, further, that, as is the case with 

 bonellin according to Krukenberg, when other acids are 

 employed the amount necessary to produce the blue colour 

 depends upon the strength of the acid, and not upon its 

 chemical nature. Thus a much larger amount of acetic acid 

 is necessary than of hydrochloric, while excess of nitric acid 

 is apt to carry the reaction beyond the blue stage, and pro- 

 duce a brown solution from which the original pigment cannot 

 be recovered. This is a product of decomposition. 



Comparison with Bonellin. — In its relation to acids 

 chsetopterin shows a marked analogy to bonellin. The changes 

 which bonellin undergoes have been studied by Krukenberg 

 (3), and his results may be briefly detailed. 



Krukenberg found that the addition of a considerable 

 amount of strong acid to a solution of bonellin turned his 

 bright green solution violet without destroying the fluorescence, 

 while a large excess turned it pure blue without any trace of 

 fluorescence. He figures three sets of spectra corresponding 

 to three stages in the action of the acid. The first of these 

 he describes as indicating the existence in the solution of a 

 mixture of bonellin and an acid derivative ; the other two as 

 representing two distinct acid derivativesj which he calls 



