tain how far animals derive their
odours in this way in a complete state from their food, and how far
they chemically construct them afresh by their own activity. No doubt
both processes occur; but in plants the odorous bodies are built up
entirely by the chemical action of the plant itself upon simple salts
of carbonic acid, ammonia and nitrates. Animals can certainly take
highly elaborated chemical bodies into their digestive organs without
destroying them and absorb them unchanged into the blood and deposit
them in the tissues. Thus the canary is made to take up the red colour
of cayenne pepper and deposit it in the feathers. Thus the green
oysters of Marennes acquire their colour from minute blue plants
(diatoms) on which they feed. And thus, too, the canvas-backed ducks
of the United States take into their tissues the odorous matter of
celery, and our own grouse the flavour of heather, whilst fish-eating
birds and whales in this way acquire a fishy taste. So, too, the
flounders and the eels of the Thames, and even salmon in muddy rivers,
acquire a taste like the smell of river mud. It is probable that many
of the odours of animals (but by no means all) are thus derived
directly from their food, or are produced by very slight changes of
the odorous bodies absorbed in food. Mutton and beef owe their savour
in some degree to the scents of the grasses on which sheep and oxen
feed. And it is not improbable that the sheep-like smell which the
Chinese detect in the European, comes to the latter direct from his
general use of the sheep as food.

Plants are the great chemical manufacturers in the world of life, and
second to them come our human industrial and scientific chemists. And
though we must claim for animals some power of manufacturing distinct
odorous bodies from inodorous nutritive matter assimilated by them, it
is probable that in many cases the odour which is characteristic of an
animal is derived by no very complicated change from odorous bodies
existing in its habitual food.

A curious case of a substance valued as perfume by civilised man, and
yet coming from a source whence sweet odours would hardly be expected,
is that which is known as "ambergris," or "ambre gris" (grey amber).
It is still used in the manufacture of esteemed perfumes, and is sold
at five guineas the ounce. It is found floating on the surface of the
ocean, and is a concretion of imperfectly digested matter from the
intestine of a whale--p