Late researches appear to show that the eggs adhering to the hair about the anus or elsewhere are eaten by lice of the same animals, and within these insects undergo further development. The dog and cat, subsequently swallowing the lice, infect themselves with the mature worms. Thus also persons, especially children, from too great familiarity with these animals, directly or through their food, may likewise become infected.
TÆNIA NANA, the Dwarf tape-worm, has been observed but once. It was discovered by Bilharz, in Egypt, in a boy who died of meningitis. It is a little worm, about half an inch in length, and occurred in large numbers in the duodenum.
TÆNIA TENELLA.—This is another small species, which has been but once observed. It is described by Cobbold, who suspects it to be derived from measles of the sheep.
TÆNIA FLAVOPUNCTATA is also a small species, from eight to ten inches long, with ripe joints about one millimeter long and from one and a half to two millimeters broad. It is described by Weinland, and has also been but once observed. A half-dozen specimens were discharged from a healthy child, of nineteen months, in Boston, Mass.
Since the above was written the author has had the opportunity of examining some little tape-worms which he suspects to be of the same kind as the former. They occurred in the practice of T. V. Crandall in Philadelphia, and were expelled from a child of three years of age after the use of santonin. About a dozen fragments appear to have pertained to three worms, from twelve to fifteen inches in length. The head in all was lost. The anterior part of the body is thread-like, the posterior part about two and a quarter millimeters wide. The width of the joints is more than twice the length. The ripe joints are pale brown, and are remarkable for the comparative simplicity of the uterus, which is distended with brown eggs. A peculiarity of the worm is the repeated but irregular alternation of fertile with sterile joints.1
1 Amer. Journ. of Medical Sciences, 1884, p. 110.
The species is probably more common than might be supposed, and from its small size, and perhaps harmless character, has generally escaped notice.
TÆNIA MADAGASCARIENSIS.—This species, described by Davaine, is imperfectly known. Fragments of the worm have been twice observed in the Comoro Islands.
BOTHRIOCEPHALUS LATUS.—SYNONYMS: Dibothrium latum; Tænia lata; Broad tape-worm.
This tape-worm, of another genus than the preceding, is a common parasite of man in certain localities of Europe, but has not been found as an indigenous product elsewhere. It occurs especially in Sweden and Russia, East Prussia, Poland, and West Switzerland. In the latter country it prevails to such an extent that it is reported that about one-fourth of the inhabitants of Geneva are thus infested. Among the tape-worms submitted to the writer from time to time for identification a few years ago was a large specimen of Bothriocephalus latus, but it proved to have been derived from a Swede who had arrived in this country only a few months previously.