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Sun Apr 10 15:49:46 EST 2005


Universal knowledge for the people.
 mk95528 at navix.net
Margie Krick and Richard Druery
Historical Information Only
(graphics (tif) are in the misc. directory)

TAPE-WORM

Tape-worm is a word popularly used in vague sense to designate any
worm of the group Cestoidea (see CESTOID WORMS). according to Dr.
Cobbold, upwards of 250 distinct forms of cestoid worms have been
described, of which probably somewhat less than 200 mat be regarded as
really good species. These he divides into the three families of (1)
Taeniadae, or true tape-worms; (2) Bothriocephalidae, and (3)
Tetrarhynchidae. For the natural history of the tape-worm generally,
we must refer to the article CESTOID WORMS. We will hear only remind
the reader of the following points necessary for the due understanding
of this article, and that every T. passes through several distinct
phases during its life-history. In the ordinary colonial or tape-worm
condition, says Dr. Cobbold, 'it has been termed the strobila (Van
Beneden). The separate joints of which the strobila is composed are
denominated proglottides, or zooids. The anterior segment forms the
head, and remains barren, those of the neck and front part of the body
being sexually immature during the process of strobile-formation. The
mature proglottides at the caudal end are capable of realizing an
independent existence, and the eggs which they contain develop the
six-hooked embryos, or proscolices (Van Beneden), in their interior.
These latter become metamorphosed into scolices or nurses,
representing the well-known cysticercal state, which, in its sterile
or aborted condition, forms the common hydatid.'  During the greater
part of their existence, the tapeworms are parasitic animals, the
mature proglottides and eggs being free only during a comparatively
short interval. They are mostly restricted in their distribution to
the vertebrate animals, comparatively few of the invertebrates
(excepting the cuttle-fish) appearing to harbor them in their adult
condition, although the T. larvae, nurses, or scolices probably abound
in various invertebrate groups.
In the human body, no less than ten species of T. occur, viz., eight
true tape-worms, and two species of Bothriocephalus ; and as four
distinct species have been found in the Barbary ape, it is obvious
that errors of diet, due to civilization, are not the cause of these
parasites. Amongst the animals with which we are most familiar, the
species are plentiful in the common dog (and in true carnivora
generally), in rats, and mice. The typical ruminants are almost
constantly infested both by mature and immature forms; while the
larger pachyderms, and solidungulates (the horse, ass, &c.) harbor
only a few adult forms; but only larvae appear to be known in swine.
These worms appear to be as abundant in granivorous birds as in
Carnivorous hawks, owls, &c. In the water-birds generally, the adult
worms are very abundant, their larvae existing in the food of such
birds, in fishes, molluscs, &c. In reptiles, these worms are extremely
rare, although other parasitic worms abound; while in fishes they are
very abundant both in the adult and larval forms.
The Taeniadae, or true tape-worm, may be distinguished from the other
families of the order Cestoidea (cestoids or tapeworms in the popular
sense) ' by the possession of a small distinct head, furnished with
four simple oval or round suctorial discs (suckers), and commonly also
with a more or less strongly pronounced rostellum (proboscis) placed
at the summit in the median line. This prominence, when largely
developed, becomes retractile, and when not in use, is lodged within a
flask-shaped cavity, lined by a sheath, and supplied with special
muscles; it is also very frequently armed with a single or double
crown of horney chitinous hooks, there being occasionally as many as
five or six separate circular rows of these organs. attention to the
number, relative size and disposition of the hooks is often sufficient
to determine the particular species. In nearly all cases, the
reproductive orifices are situated at or near the margins of the
joints which are bisexual.' The eight true tape-worms accuring in man
are (1) Taenia solium, Linnaeus; (2) T. mediocanellata, Kuchenmeister;
(3) T. acanthotrias, Weinland; (4) T. flavopuncta, Weinland; (5) T.
nana, Von Siebold; (6) T. elliptica, Batsch; (7) T. marginata, Batsch;
(8) chinococcus, Von Siebold.
The common tape-worm, taenia Solium, derives its Linnaean title from
the idea  that it is always a solitary worm. Although this is
commonly, it is not by any means always the case: Kuchenmeister has
several times found two or three together, and cases are recorded in
which 30 and even 40 worms have been expelled from one patient. The
full-grown T. (strobila) has been known from the earliest times, and
is described by Hippocrates, Aristotle, and Pliny; but its
organization and mode of development have only been properly
understood during the last few years. The segments of which it is
composed vary in size, and number from 800 to 1000, the earlier
immature ones being extremely narrow, and the sexually mature joints
commencing at about the 450th segment. From 10 to 35 feet may be
regarded as representing its ordinary length; its breadth at about the
widest part being one-third of an inch. The head, which is seldom seen
in the tape-worms exhibited in our museums, although the evacuation of
the head with the rest of the worm is not very rare, is very small and
globular (about the size of a pin's head), with black pigment
ingrained in it.
On examining it with a low magnifying power, it displays four circular
sucking discs, in front of which is a conical proboscis, armed with a
double crown of hooks, from twenty-two to twenty-eight in each
circular row. The head is succeeded by a very narrow neck, nearly half
an inch in length, which is continued into the anterior or sexually
immature part of the body, in which traces of segmentation first
appear in the form of fine transverse lines, which are gradually
re-placed by visible joints. These joints or segments contains both
male and female organs of generation; and in addition to these
structures, the entire series of joints is traversed by a set of
vascular canals constituting the so-called aquiferous system, which
consists of two main channels, one passing down on either side of the
worm, and both being connected by transverse vessels, which occur
singly at one end of every joint. It is only in the alimentary canal
of man or some other animal that a T. of any kind can attain to sexual
maturity; and in all of these the eggs are fecundated before being
discharged.
The expulsion of the eggs may take place in any of the following ways:
First, the mature segments separate from each other, and passing out
of the body, either with the ordinary evacuation of the bowels or
independently, become decomposed, and set free the enclosed eggs. The
single joints thus discharged undergo violent contraction after being
expelled, which led to their being formerly mistaken for a distinct
species of worm, to which the title Vermes cucurbitini was applied,
from their resemblance to a pumpkin seed. 
Examining the recently discharged excrement of a constipated dog, the
same phenomenon may be very frequently observed. Secondly, the eggs
may be discharged through the genital pore by pressure from any cause.
It is only thus that we can account for the occasional co-existence of
a Cysticercus cellulosae (the embryo of the worm) and an adult T. in
the intestinal canal of the human subject - an association which
constitutes one of the most serious dangers which the matured worm can
inflict upon the host, and one of the strongest indications for its
removal. Thirdly and lastly, the mature joints sometimes appear to
undergo disintegration within the intestine, and to liberate the eggs;
but the conditions under which this disintegration occurs are unknown.
In reference to the ultimate fate of the embryos in ovo, that are
liberatedin the intestinal canal, Dr. Cobbold has informed the author
of this article in a private communication, that, in his opinion, they
do not migrate in the living host, except when by regurgitation they
occasionally get into the stomach, when after their shells have been
dissolved by the gastric juice, the young organisms commence their
wanderings. The mature segments are usually expelled from the human
bowel at the rate of six or eight a day. Their vitality is prolonged
by moisture, which favors the distribution of the liberated eggs over
grass and other vegetables, or in water, which may be used as food or
drink by animals. For a full description of the eggs, we must refer to
Dr. Cobbold's work. It is sufficient here to remark, that, in their
mature condition, they 'present a globular figure,and are easily
recognized by their remarkably thick shell, which surrounds the
six-hooked embryo. They present an average diameter of 1/694th of an
inch, the shell itself measuring about 1/4000th of an inch in
thickness. After a while, by accident, as it were, a pig coming in the
way of these embryos, or of the proglottides, is liable to swallow
them along with matters taken in as food.
' The embryos, immediately on their being transferred to the digestive
canal of the pig, escape from the egg-shells, and bore their way
through the living tissues of the animal, and having lodged themselves
in the fatty parts of the flesh, they restto await their further
transformations or destiny. The animal thus infected becomes measled,
its flesh constituting the so-called measly pork. In this situation,
the embryos drop their hooks, and become transformed into the
Cysticercus cellulosae. A portion of this measled meat being eaten by
ourselves, either in a raw or imperfectly cooked condition, transfers
the cysticercus to our own alimentary canal, in which locality the
cysticercus attaches itself to the wall of the human intestine, and
having secured a good anchorage, begins to grow at the lower or caudal
extremity, producing numerous joints or buds to form the strobila or
tapeworm colony.' In its fully mature stage, the measle presents the
appearance of an elliptical hydatid, varying in size from that of a
pea to that of a small kidney-bean, the average diameter being
one-third of an inch. On dissecting or breaking up a measle, it will
be seen that  the great vesicular portion constitutes the bladder-like
caudal extremity of the cysticercus, while the head, neck, and body
can be drawn out so as to exhibit a vermiform character. 


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