or a man would have to be separately prepared and
"immunised" by habituation for every distinct kind of poison. We now
know that this is not the usual way in which Nature confers immunity
to poisons. Most astonishing, and at first sight magical or
mysterious, powers exist in the living protoplasmic cells in and
around the blood of man and higher animals, which enable their
possessors to resist and combat the poison-producing microbes, and
also the poison itself, of all kinds, by which the race is liable to
be attacked.

Few of us realise what a wonderful and exceptional fluid the blood of
a higher animal is. The Australian natives attach so little importance
to it that they actually cut themselves and use their blood as a sort
of paste for sticking decorative feathers on to a pole! The Papuans
are more advanced, since they regard the flow of blood from a cut or
graze as an evil portent. And some respect to the greatness and wonder
of blood is shown by those persons among civilised peoples (more
frequently men than women) who faint when they see blood, or even at
the mention of its name! This stream of red fluid within us (of which
an average man has about fifteen pints in his vessels) courses at a
tremendous rate from the heart through all the endless branches and
networks of arteries, capillaries and veins, and back to the heart. It
feeds, cleanses, warms and takes "vital air" (the old name for oxygen
gas) dissolved in it to every particle of our bodies, fresh and fresh
at every pulse-beat as it rushes on. It not only absorbs crude
digested food through the walls of the gut, but conveys it to where it
is worked up and distributes the worked-up product. It removes the
quickly used-up substances from every part, and the choke-damp or
carbonic acid which would stop the whole machine, and kill us, were it
not got rid of through the lungs as the blood hurries through the
walls of these air-sacs, whilst other used-up materials are carried by
it to the kidneys and passed out of the body through them. Every part
of the body is brought into common life with every other part by this
impetuous blood-stream--which is here, there, and everywhere, right
round, and back again, in twenty-five seconds! It is obviously a very
serious thing if a poison-producing microbe gets into this
blood-stream and multiplies within it, or if poison-producing microbes
lodge somewhere beneath the skin in a wound, and keep on discharging
virulent pois