thus producing grave
mischief.

The _thread-worm_ is the commonest variety of these creatures, and has
the peculiarity of inhabiting the lowest twelve inches of the bowel,
where it produces much irritation and causes very distressing itching.
It is often present in great numbers, and is so rapidly reproduced, that
in a week or two after it has been apparently got rid of, it may again
be found as numerous as before. Certain articles of food seem to favour
its development, such as pastry, sugar, sweets, beer, fruit, and
anything which is apt to undergo fermentation, and thereby to impart to
the evacuations a specially acid character. These worms are often
accompanied with more or less marked symptoms of indigestion, but
otherwise the local irritation is usually the only indication of their
presence. They produce, indeed, such disturbance of the nervous system
as may attend indigestion in any of its forms, but I have never but once
known convulsions occur apparently due to their presence in great
numbers, and ceasing on their expulsion; and this was in a child between
eighteen months and two years old.

The _tape-worm_ is developed in the human body from a minute germ or
ovum; one form of which exists in the flesh of the bullock, the other in
that of the pig; and which seems to require for its growth the favouring
conditions of warmth and moisture which are found in the intestines. It
fixes itself to the lining of the bowels by means of its mouth, which is
furnished with minute tentacles, and it thus derives its support from
the juices which it imbibes. The head is so small as not to be seen
distinctly without a magnifying glass; and immediately beyond it the
jointed body begins; at first, scarcely bigger than a thread of worsted,
but gradually enlarging, till at the distance of three inches it is an
eighth of an inch wide, and thence rapidly widens till each joint is
half an inch wide, and from a third to half an inch apart. It does not
exceed these dimensions, even though it may grow to the length of four
or six yards. Portions of it, sometimes a yard or two in length, are
thrown off from its lower end occasionally, and this occurrence often
gives the first indication of its presence, the worm continuing to grow
as before, and fresh portions being detached from time to time. It does
not appear that the worm has the power of reproducing itself; hence its
French name of _ver solitaire_, and the occasional presence of two