Trematodes (Sucking-worms). — The trematodes when fully developed are found, with but few exceptions, in verte brate animals. The first host is usually a mollusk.
The DISTOMA HEPATICUM, or LIVER LEECH, is a leaf-shaped sucking-worm, 28 millimetres in length and 12 millimetres in width. The eggs are ovoid in shape, 0.13 millimetre in length, and 0.08 milli metre in width, from which an embryo develops in water and attaches itself to a host of the mollusk family. Leuckart says the young of the liver-leech are protected by the limnaaa in marshes in the form of radim or germ-sacks, in which appear later on germ-granules. From these are developed cercariie, resembling tadpoles. When these are taken into the digestive tract of ruminant animals, or, as rarely happens, into man, they enter the bile-ducts and sometimes the intes tine or inferior vena cava. When these parasites are present in animals,—which sometimes occurs and in great numbers, —the bile-ducts are obstructed, ulcerative strictures or dilatation is produced, bile concretions are formed, and inflamma tory changes are established in adjacent structures or changes produced in the parenchyma or glandular tissues. The endemic fluke disease occurring in Japan is characterized by hepatic enlargement, emaciation, diarrhoea, and, frequently, ascites.
The DISTOMA LANCEOLATUM likewise occupies the biliary passages in sheep and cattle, where it occurs in small numbers and occasions no important changes; if in greater numbers, disturbances are pro duced in the structures of the liver. It is very rare in man.
The DISTOMA ELEMATOBITIM, OT BLOOD FLUKE, is very common among the inhab itants of Egypt, one-fourth of whom are said to suffer from its effects; it also occurs in Zanzibar, Syria, and Sicily. The male is from 12 to 14 millimetres in length; the female, 16 to 19 millimetres in length. They lie, as a rule, in close contact, the female in the canalis gynce cophorus of the male. The eggs are of an elongated oval, 0.12 millimetre in length, with a terminal or lateral spine.
Small crustaceans act as the inter mediary host into which the ciliated em bryo bores its way and becomes capsu lated. Infection probably occurs through
drinking water containing the larva;. The parasites are found in the portal vein and its branches, the splenic and mesenteric veins, and in the blood-vessels of the bladder and rectum. The eggs, traversing the mucosa and submucosa, reach at times the liver, lungs, kidneys, as well as the bladder and rectum, giving rise to irritation, ulceration, concretions, and neoplasms. The first and most con stant symptom is luematuria, which grad ually leads to anmia.
As to treatment, the extract of male fern internally is considered of value by Fouquet.
The DISTOMA PULMONALE, Or BRON CHIAL FLUKE, is a club-shaped parasite about S to 10 millimetres in length. It is found in China, Japan, and Formosa, where, according to Ringer and Manson, it causes an epidemic disease. It is lo cated primarily in the lung, its presence resulting in cough, ha2moptysis, and the occurrence of small flukes in the expecto ration.
Cestodes (Tape-worms).—Cestodes are flat worms about the size and color of a fragment of white tape, devoid of mouth or intestine. They increase by alternate generation, through the germination of a pear-shaped primary host (scolex, or head), and remain attached to it for some time as a long, band-shaped colony. The sexually-active members of this col ony. or proglottides, increase in size the farther they are separated from their place of origin, by the formation of new members, but they have no other out ward peculiarity.
The pear-shaped primary host (scolex, or head) has from two to four suckers, and is provided also with claw-like curved hooks. By means of these adhering or gans the tape-worms fasten themselves to the intestinal wall of their immediate host, which is always one of the verte brate animals. The scoleces develop from a round embryo with four to six hooks, and arc found as so-called "mea sles," chiefly in parenchymatous organs. Later by means of passive migration they move out of these organs into the intes tine of their future host.
Tape-worms which occur as parasites in man belong to different families known as (1) the twnia and (2) the bothriocephali.