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

Animals Parasitic in Man
off portions of it with its teeth, or it may penetrate into the
wall of the small intestine till it reaches a small blood vessel.
Fig. 5. A human hookworm sucking in and nibbling
the lining of the small intestme of nlan
It then injects into the host substances, called anticoagulins,
which delay or prevent the clotting of the blood, so that a
plentiful supply of blood is available. The blood thus sucked
from the host is passed quickly through the food canal of the
hookworm and out again at the anus, which is near the posterior
end of the worm’s body, but not, as it is in the earthworms
and their relatives (Annelida), at its posterior tip. The
amount of blood thus removed from the host is further discussed
in chapter 12. It may be considerable and the loss of it
causes the anaemia which is a prominent symptom of the
disease caused by hookworms. We do not know what use the
hookworms make of the blood that they remove. Because they
usually suck blood from small arteries rather than from small
veins, it seems probable that they use the respiratory pigment
(haemogZo6in) in the blood for their own respiration and that
the blood is therefore not sought as food, but to enable the
worms to breathe.
Hookworms belong to the family of roundworms called the
Ancylostomatidae. The following species of this family may
be parasitic in the smail intestine of man:
Ancylostoma duodenale
This is a greyish-white species, but it is reddish when it has
been sucking blood. The males are 8 to 11 mm. (& to&inch)
and the females 10 to 1 s mm. (& to 4 inch) long. The males
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