Page:The American Cyclopædia (1879) Volume VI.djvu/679

 ENTOZOA 667 nal canal of carnivorous mammalia. Thus man obtains the tcenia solium from swine ; the dog the T. serrata, T. cwnurus, and T. echinococcus from the rabbit, the sheep, and the ox re- spectively; the cat the T. crassicollis from the mouse ; and so on. Second, the malacolepidota, or soft-shelled tapeworms, the eggs of which are to be hatched in the stomach of articulata and mollusks. The mature entozoa of this or- der inhabit the intestinal canal of such ani- mals as prey upon the above, as fish, birds, and insectivorous mammalia. Trematoda, ste- relmintha (Owen), isolated flat worms. These entozoa are characterized by their flattened, more or less elongated shape, and by ventral sucking disks. The same individual possesses the organs of both sexes. Rudolphi divided them into different genera, according to the number of cup-like suckers present. This classification has been given up, inasmuch as the more important distinctions of structure did not correspond to the external markings ; but many of the names have been retained. Thus the distoma Jiepaticum, or liver fluke, has two sucking disks. This, the best known of the trematode worms, resembles much a cucumber seed in form, and measures in length one inch, in width about half an inch. It is yellowish brown, probably owing to the bile in which it lives. In this class we first find evidence of an alimentary canal, in addition to the sex- ual organs, which gives it a higher rank than the cestoi- dea. This consists of a tri- angular opening or mouth, which may be used either as a sucker or means of ob- taining nutriment. From this rises the intestinal ca- nal. An excretory system is also present. This fluke has been found only in a few well authenticated cases in man. Its true home is in the gall ducts of sheep, and it is generally found in the same place in the human system. Cases are on record in which it has been found beneath the skin, having made its way thither by boring into the epidermis. In the liver of the lower animals it works sad havoc in autumn and winter, causing a dilatation and catarrh of the gall ducts, and an interference with the hepatic function, by which, of course, the secretion of the bile is disturbed and changed. They may occur in such quan- tities as to stop up the cystic duct, and their eggs are deposited in vast numbers in the bile. The symptoms they create in man need not be stated here. The passage of this worm by the stomach or intestines is the only proof we could have of its presence be- fore death. The generation and development FIG. 7. Distoma he- paticum. of these worms had been a subject of great in- terest to naturalists, since Steenstrup made them the object of investigation in illustrating his theory of alternation of generation. The eggs of the distoma, escaping in the form of ciliated embryos, become converted while in the water into nurses or grand- nurses ; that is to say, they are not themselves developed into young distomata, but produce in their interior several new or- ganisms, which latter are the real young or larvaa of the future animal. These nurses are sup- plied with organs of self-sup- port. The young brood, known as cercarice, possess in some spe- cies tails by which they under- take wanderings on their own account, become attached to mollusks or like animals, and thus find their way into the in- testine and liver of some larger animal. The tailless brood have the power of encysting them- selves while in the water, and may thus be borne about till they are swallowed by some of the herbivora. This is the gen- eral plan of development in all trematode worms, but it is not yet known what peculiar meta- morphoses this entozoon un- dergoes. There can be little doubt, however, that sheep in- fect themselves by devouring snails which frequent the grass in moist mea- dow pastures, or by drinking ditch water. Whether " the rot " is actually caused by this parasite is not absolutely certain, though highly probable, as they are always found in this dis- ease. Little benefit is to be derived from the use of anthelmintics, but a proper attention to these laws of prophylaxis will aid the farmer much in preserving his flocks in a healthy condi- tion. The distoma hcemato- Mum forms a very common disease in man in Africa, ac- cording to Bilharz, who found it first in the blood of the portal and mesenteric veins. But its chief habitation is the bladder and intestines, and when present in numbers it is very detrimental. In the blad- der the worms fasten them- selves to the mucous mem- FIG. 9. Cercaria of brane, and produce patches TYia+/ma JumfvH, C _. of inflammation, exudation, and hsemorrhage. The fun- gous excrescences thus caused are peduncu- lated, and often of the size of a pea. Within them the animals may be found, and on their external surface the eggs. In the ureters the inflammation they create is sufficient to pro- FIG. 8. Ciliated Embryo of Distoma.