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

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Animals Parasitic in Man
phases differ from those of the hookworms because they are
passive, not active, so that their entry into the host’s mouth
depends either on chance or on the actions of a host which neglects
to make sure that these passive infective phases have not
got into its food or drink.
Entamoeba histolytica
This species (fig. 6) is in every respect quite different from
the hookworms just described. It causes in man the disease
called amoebic dysentery. It is one of the singleeelled Protozoa
and it belongs to the class of this phylum called the
Rhizopoda, whose bodies are not enclosed in definite envelopes
that preserve a definite shape; they are always changing
their shape and they do this by putting out extensions of the
substance of the body called ps&@Ldia, into which the rest of
the body then moves, so that the organism can in this manner
move along. The pseudopodia also enclose and take into the
body, bacteria, and other small unicellular organisms on
which the Rhizopoda feed. These particles, wher, they are in
the body, are enclosed in spaces calledfood-vacwlles, into which
digestive ferments are secreted. Undigested remains are cast
out at any point on the surface of the body. Inside the cell=
body there is a structure called the 9tz&us, which contains a
specialized kind of protoplasm called chromatin. The nucleus
governs the life of the cell and the organism cannot live without
it.
The life history of Entamoeba hz’stolytica is relatively simple.
The phase of it that corresponds to the adults of other parasitic
animals is called the trophozoite, a feeding-phase. It lives in the
large intestine of man; and also in the large intestine of macacque
monkeys (genus Muzczls). Natural infections with it
have been found in dogs and these have probably been derived
from man. If cats are infected with it by man, it will live in
them, especially in kittens; but natural infections of cats do not
occur.
E&amoeba histoljtica is an amoeba of microscopic size. It
measures 10 to 40 (average 20 to 80) micra in diameter,’ one
micron being one thousandth of a millimetre or about nh
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