Page:The American Cyclopædia (1879) Volume VI.djvu/678

666 ENTOZOA Various other taenisB infest man in one of their stages, the most dangerous of which is the eckinococcus, or encysted form of E. hominis. The cysts produced by this parasite are often as large as a man's head, causing great suffering and death. In Iceland every seventh person FIG. 5. Taenia echinococcus. a. Cyst, opened. 6. Collection of Vesicles or Scolices. c. Single Scolex greatly magnified. is thus afflicted. The explanation lies in the filthy habits of this people, and in the great number of dogs they keep, which assist in spreading the seeds of the disorder. Here the cysts or hydatids contain instead of one scolex or head innumerable embryonic forms, which of course increases the risk of infection. The mature tapeworm produced artificially consists of but three joints, and on this account has hitherto escaped notice. Even now it is not known whether man himself or dogs are the hosts of the mature helminth. Another re- markable species dwelling in the intestinal canal of man is the bothriocepkaliis latus, or broad tapeworm. This differs from the true FIG. 6. Bothriocephalus latus, with View of Tail, magnified. taenige in the construction of its head and joints. The former is oval, flat, and instead of a coro- net of hooks and round suckers possesses two longitudinal sucking grooves on each lateral margin, by which it fixes itself; the latter are one third of their width only in length, and the genital opening is found on the middle of each joint, instead of at the lateral margin, as in tsenise proper, and occurs on the same surface throughout its whole length. They are sometimes as many as 2,000, but even then they do not make up a worm more than 20 ft. long. Thus far this parasite has been found in man only in its mature state. Its geograph- ical distribution is limited to Russia (including Poland), Switzerland, Italy, and the maritime districts of France and north Europe, and it most probably undergoes its transitional stage of development outside the human intestine in some of the mollusks, which form the food of man. A few other species of tapeworm infest mankind, but they are seldom met with, and will be found enumerated in the accompanying catalogue. The dog, from his domestic and om- nivorous habits, is made the host of many of these entozoa, and does much to keep up their precarious existence. Without his aid the tcenia cosnurus would undoubtedly become extinct, and thus the sheep breeders would be rid of a disease which often proves so fatal to their flocks, viz., the staggers. This disease is caused by the presence in the brain of hydatids or cystic ccenuri, which when eaten by butcher and sheep dogs are converted into the corre- sponding tasnia, the embryos of which are in turn scattered broadcast over the pastures, where they find ready admission to the grazing herds. This too has been made the subject of searching investigation in Germany, and shep- herds are taught to keep their dogs free from this tapeworm, by putting out of their reach the flesh of animals afflicted with the staggers. Sheep may often be kept healthy by keeping them from moist -places, and from pastures while the dew is still on the grass, for the pro- glottides seem to seek such localities, and the heat of the sun appears destructive to their vitality. Much more good may be effected by such preventive measures than by adminis- tering anthelmintics, or by attempting the re- moval of the cysts by the trephine or trochar. Very often immense droves of swine have to be slaughtered on account of the measles, and such attacks always prove that the victims have lately been in the neighborhood of some person who has a tcenia solium. Wild swine are never affected in this way. Occasionally this variety of cys- ticercus is found in the flesh of other animals eaten by man, as the ox, deer, and bear, but very seldom. No doubt a great deal of measly pork is sold both fresh and salted, and enough is eaten in an uncooked state in the form of sausages, raw pork, and the like, to account for the wide distribution of tseniae. Dr. Weinland, in his essay on human cestoidea (Cambridge, 1858), divides the ta- nioidea into two classes: First, the sclerolepi- dota, or hard-shelled tapeworms, the embryos of which, developed in the warm-blooded verte- brata, become mature tasnia) only in the intesti-