126 
COLOUR IN NATURE 
CHAP. 
in the epidermis of Astacus but not of Homarus or 
Nephrops , 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 dilute 
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 presence 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. 
