Animals P by: Geoffrey LaPage Published by ... - PSSurvival.com

I
Animals Parasitic in Man
host, so that they are passing through its digestive canal. The
faeces or urine of man, for example, mzy contain not only the
eggs and other phases of parasites that cannot be parasitic in
man, but even such non-parasitic organisms as the caterpillar
or pupae of insects, or even adult insects that are not parasitic
in any animal. There may also be seeds, imperfectly-digested
remains of food, starch-grains, and other objects that may resemble
parasites or phases of their life histories. To all these
objects, whether they belong to parasitic or non-parasitic
species, or to the food of the host, the general name pseudoparasites
is sometimes given.
We are now in a position to say, as precisely as we can,
what a parasite is. A parasite, we can say, is a living organism
which establishes a physiological association with the tissues
on the surface of, or inside, the body of another organism,
which is usually bigger and stronger than the parasite and always
belongs to a different species, the purpose of this association
being primarily to provide food for the parasite; this
other organism is called the host of the parasite and the host
always suffers, as a result of its association with the parasite,
some degree of injury and always reacts to some degree
against the parasite and the injury that it suffers.
This definition is, we must admit, not entirely satisfactory.
It attempts, as all other definitions of living organisms do, to
confine, in a static framework, something that is slowly and
continuously undergoing change. It does, however, focus attention
on the parasitic animals that are the subject of this
book. It gives us, however, no hit of the variety and complexity
of the world of parasites, nor of the beauty of the
structural and physiological adaptations that they show; nor
even, on the other side of the picture, of the long history of
pain, suffering, and death for which parasitic animals are responsible.
Man, in this book, is the host with which we are
primarily concerned; and man, like other animals, has suffered,
without a doubt, from parasitic animals since the earliest days
of his history. There is no part of his body, nor, indeed, any
part of the bodies of the hosts of parasitic animals in general,
which is not visited by some kind of parasitic animal at some
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