II 
THE PIGMENTS OF ORGANISMS 
39 
4. Reserve Products 
The next group of pigments includes those which 
are actually reserve products or are associated with 
such. Although the literature of the subject contains 
numerous mention of pigments described as reserve 
products, it is still doubtful whether the description 
is accurate in any one of the cases. Carminic acid, 
the pigment of the coccus insect, is very frequently 
described as a reserve, but this is doubtful ; it is a 
glucoside, and therefore a carbohydrate is produced 
by boiling it with dilute acid, but nothing is certainly 
known as to its function. 
The term reserve product is applied with more 
plausibility to various members of the large series of 
lipochromes or fat-pigments. The lipochromes are 
pigments, varying from yellow through orange to red 
in colour, which in the dry state give a blue colour 
with concentrated sulphuric or nitric acid, and which 
are soluble to a greater or less degree in all the 
solvents of fats, as well as in fats themselves. They 
are divisible into two series, according as they do or 
do not form compounds with the caustic alkalies. 
Both series occur in animals, but the second only in 
plants. In plants the best known lipochrome is 
carotin, which is widely distributed, and is, according 
to Carl Ehring, a cholesterin fat. The chemical 
nature of the other series is still unknown. 
The lipochromes occur frequently, though not 
invariably, in association with fat in organisms. 
From the red flesh of the salmon, for example, it 
is possible to extract an oil containing the pink 
