Larval condition: Cysticercus saginata; Beef measle-worm.
This, which is now regarded as the most common tape-worm of man, is named the beef tape-worm because it is derived from the beef used as food. In the mature condition it lives only in the small intestine of man, and in the juvenile condition it lives in the ox. Its frequency is proportioned to the prevalence of the custom of eating beef in a raw or insufficiently cooked state, conjoined with the careless habit of leaving human excrement in pastures where it is accessible to cattle.
The mature beef tape-worm is commonly observed as a soft, yellowish-white, thickish, band-like worm, ranging from six to twenty feet or more in length. The head, about the size of a yellow mustard-seed, is rounded quadrate and provided with four equidistant hemispherical suckers. Succeeding the head is a short, slightly narrower, flattened neck, which merges into the gradually widening and segmented body. The segments, at first narrow fore and aft and several times wider than the length, become successively larger, proportionately longer, more distinct, and quadrate in outline; and finally the length may exceed the breadth two or three times. A full-grown tape-worm may possess twelve hundred segments and more, and specimens are recorded as reaching a length of thirty feet. The larger segments measure from a quarter of an inch to an inch long and from three to four lines wide. The larger or riper segments exhibit on one border, irregularly alternating on the two sides, at or near the middle, a papilla in which is the external aperture of the genital apparatus. In the fully-ripe segments the uterus, distended with eggs, may be obscurely seen through the wall of the body, but is rendered more visible by drying the segments, moderately compressed, between two pieces of glass. It appears as a long, narrow, white or brownish median line or tube, giving off laterally numerous short, transverse, more or less branching tubes.
The worm in its usual position lies along the course of the intestine in loose coils, and exhibits lively movements, alternately shortening and elongating, expanding and contracting the head, and protruding and retracting the suckers. The ripe segments spontaneously detach themselves, and may be found scattered along the large intestine ready to be discharged with the excrement, or, as is sometimes the case, they may spontaneously creep from the anus. Rarely more than a single worm infests a person at the time. The species is of rapid growth. According to Perroncito, quoted by Cobbold, a mature worm was reared from a beef measle, swallowed by a student, in fifty-four days.
It is estimated that the number of eggs in the mature segments of the beef tape-worm amounts to about 35,000. As the full-grown worm may consist of 1200 segments, and there is reason to believe these are renewed several times annually, we learn that the whole number of eggs produced by a single individual is enormous. The ripe segments, attached to the parent or becoming spontaneously detached, lay their eggs in the intestine to be discharged with the feces. When more or less emptied they shrink and appear reduced in size, and in this condition are expelled or spontaneously creep from the anus. If the ripe segments are forcibly expelled and are alive, they will lay their eggs in the feces externally. The ripe eggs are brown, oval, about 0.03 mm. long, and have a thick shell, with an outer vertically striated envelope.
As previously intimated, the common source of the beef tape-worm in man is the use of raw or insufficiently cooked beef affected with measles. The ox becomes infested by swallowing the eggs, or, it may be, even the entire segment, of a tape-worm deposited with feces in the pastures of cattle. The measles usually occur in the muscles, including the heart, though they have also been noticed in the liver and lungs. They appear, in beef, as oval, whitish bodies from the size of a mustard-seed to that of a pea. They consist of a sac of connective tissue containing the larval tape-worm or cysticercus. Measles under ordinary circumstances are seldom noticed in beef, and when they occur are commonly few in number.
According to the latest authorities—Leuckart, Cobbold, Stein, and others—the beef tape-worm is the most common of the cestodes which infest man. Until within about thirty years it was generally not distinguished from the pork tape-worm, and this was accordingly regarded as the most common human species. Since the writer distinctly recognized the beef tape-worm within the last twenty years, all the specimens of Tæniæ, from people of Philadelphia and its vicinity, that have been submitted to him for examination—perhaps in all about fifty—have appeared to belong solely to Tænia saginata. The prevalence of this species with us is no doubt due to the common custom of eating underdone or too rare beef, while the pork tape-worm is comparatively rare, as with us pork is only used in a well-cooked condition.
TÆNIA SOLIUM.—SYNONYMS: The Pork tape-worm; Solitary tape-worm; Armed tape-worm.
Larval condition: Cysticercus cellulosæ; Pork measle-worm.
Until a recent period this species was generally regarded as the most common tape-worm of man—a view which in great measure was due to the circumstance that the beef tape-worm was not distinguished from it. It was called the solitary tape-worm, still expressed by the specific name, from the impression that it rarely occurred otherwise than single at a time in a person. This has also proved to be incorrect, likewise due to the two kinds of tape-worms having been confounded together; for while the beef tape-worm most commonly occurs solitary, the pork tape-worm not unfrequently occurs with several together.