also from a gland in front of the eye (similar
glands occur in other strange positions), which has not a smell
familiar to man--that is to say, not one which has been recognised and
described--yet seems to be readily "smelt" by the animals of its own
kind. The bats--especially the large frugivorous bats--have a very
unpleasant, frowsy smell.

An important fact about animal smells is that many which we might be
inclined to attribute to the animal which diffuses them, are really
due to the fermentative or putrefactive action of bacteria which swarm
on the skin and in the intestines of animals. It is often difficult to
decide how far a peculiar animal odour is due directly to a substance
secreted by the animal, and how far the odour of that substance is
modified or even entirely produced by the chemical changes set up in
secretions of the body-surface by bacteria. Several distinct repulsive
smells liable to occur on the human body are due to want of
cleanliness in destroying bacteria by proper antiseptics. The fatty
and waxy secretions of the skin are often decomposed by bacteria, even
before complete extrusion from the glands in which they are formed,
whilst the decomposition of food in the mouth and intestines by
bacteria alters materially both the natural odour of the animal's
breath and the smell of the intestinal contents. In young and healthy
animals in natural conditions there is some check--it is not easy to
say what--upon the putrefactive activities of the omnipresent
bacteria. The skin of a healthy young animal has a pleasant odour,
and its breath (notably in the case of the cow and the giraffe) is
naturally sweet-smelling. The same should be the case, under perfectly
healthy conditions, with human beings.

There is one important cause of animal odours and flavours upon which
I have not hitherto touched. Many animals acquire an odour or flavour
directly from the food upon which they feed. Certain odorous bodies
are in the food and are taken up into the blood of the consuming
animal unchanged, and are then thrown out by secreting glands on the
skin. This is the case with the odorous substance of onions. People do
not smell of onions after they have eaten them in consequence of
particles of onion remaining in the mouth. The volatile odoriferous
matter of the onion is absorbed into the blood. It passes out first
through the lungs and later through the small fat-forming glands in
the skin. It is difficult to ascer