126 COLOUR IN NATURE chap. 



in the epidermis of Astacus but not of Homarus or 

 Nepkrops, and in the shells of the two first but not 

 the last. From the epidermis of Astacus the blue 

 pigment can be readily dissolved by water, or better, 

 a dilute saline solution. From the shells of the 

 lobster or Astacus the blue pigment can be ex- 

 tracted by treatment with a dilute solution of 

 ammonium chloride, or better, with very ailute 

 hydrochloric acid. The solution from the epidermis 

 is a very bright Prussian blue ; that from the shells 

 is usually paler, as it is more difficult to obtain a 

 concentrated solution in their case. We cannot 

 here discuss all the properties of this blue solution. 

 It may be sufficient to say that the blue colour is 

 very fugitive, and that the solution invariably 

 contains traces of albumen. Agents such as heat, 

 acid, alcohol, etc., which destroy the blue colour, 

 turn the solution pink. The pink colour is due 

 to the presehce of the red lipochrome, which can 

 be so readily extracted from the epidermis. From 

 the reactions of the blue solution I have come to 

 the conclusion that the blue pigment is a compound 

 of the red lipochrome with a complex unstable 

 organic base perhaps derived from the muscle, and 

 possibly of the same nature as the so-called muscle 

 extractives. The usefulness of dilute saline solutions 

 in obtaining the blue pigment is probably due to the 

 fact that these solutions dissolve out some proteid, 

 and the lipochrome compound is soluble in these 

 solutions (see above). The compound is readily 

 destroyed by various reagents and then the red 

 lipochrome reappears. 



Next as to the green pigments of the Crustacea. 



