AS'CABIS, a genus of entozoa, or intestinal worms, of the order nematmilea of Zedar, Cuvier, etc., and of the division sterelmintha of Owen. The ascarides have a body approaching to cylindrical, but thickest in the middle. They inhabit the intestines of animals. The species are numerous. One of the best known is A. lumbrieilides. often called the common round worm, which occurs in the intestines of man and of some of the lower animals, as the hog., AN, horse, etc., and which often occasions severe disease, and sometimes death, particularly when it ascends from the intestines to the stomach. Its presence even in its most ordinary situation in the small intestines, is attended with unfavorable effects upon the general health; and the greater the number present—wldch, however, is not usually large—the greater, of course, is the injury; although when they remain in the intestines, worms of this species are less injurious and less than other and even much smaller intestinal worms. In subjects otherwise diseased, they occasionally find their way out of the intestines into the closed serous cavities of the body, and even pass through ulcerated parts of the external integument; but the mouth is formed only for suction, and is provided with no means of boring through the healthy intestine. An immense number of remedies (anthelmintics or vermifuges) have been proposed and used in order to expel this parasite, some of which are very effectual. They do not in general kill the worms, but act by making their dwelling-place dis agreeable to them (sec VERMIFUGE). It is, however, remarked by Kilchenmeister, in his work on parasites, that the treatment of cases of this description is as yet purely empirical, because, although there must be a condition of the intestinal canal which favors the thriving of worms, we are by no means certain m lint it is.
The A. lumbrieoides is ordinarily, in size and appearance, pretty much like the common earthworm (lumbricus terrestris), from which resemblance it has received its specific name, although the resemblance is rather in general form than in more essential charac teristics. It has been seen 15 in. in length. Its mouth consists of three fleshy tubercles, which can be spread oat upon the intestine to form a broad circular sucker, and within which there is a small tube capable of being protruded. The alimentary canal consists of a muscular gullet and stomach, and a tlun-walled intestine. Between the muscular layers of the body is produced a pale reddish oily matter, with a strong and very peculiar odor, which is aradually communicated to spirit in which the worm is preserved. The
males are smaller than the females, and much more rare. The females produce eggs in great numbers; but it is uncertain if ever they are developed within the intestine in which the parent worm resides. They are certainly capable of being developed elsewhere, and probably the young enter the intestines of the animals of which they are eventually to he the parasites, after having spent a certain stage of their existence in very different circumstances: the worm in a very young state having never been found in the intestines of man or of quadrupeds, the situation of its perfecCdevelopment. The inhabitants of damp valleys are believed to suffer more than others from the A. lumbrieoldes. It is said also to be particularly frequent in persons who are much accustomed to eat raw leaves and roots; and it has been supposed that the young may exist, perhaps in an encysted state, in the bodies of insects or other very small animals which are accidentally eaten along with such food, as the young tapeworm finds its way into the human intestines from its residence as a creature of very different size and form in the flesh of the sheep or the pig. The once prevalent idea of the equivocal generation of these worms is now completely abandoned.
A. vermicularis is another species usually referred to this genus, and is the only other species troublesome to mankind. It is known as the thread-worm or maw-worm, and is very common both in children and adults. It infests chiefly the lower part of the intes tines, and particularly the rectum, great numbers being often present together, and occa sioning intolerable itching, irritation, and loss of sleep, although there is not in general much serious i Amy to health. The same anthehnintics employed against other intestinal worms are found efficacious also in the expulsion of this; and clysters are often employed with great success. The thread-worm is white, not more than half an inch in length, the male much less. Some recent authors of high reputation have separated this species from A., and call it oxyuris vermkularis, but the term asearides is often employed in medical works with exclusive reference to it; and indeed this name, derived from the Greek askarizo, to jump or move briskly, probably owes its orgin to the liveliness of motion which this species exhibits. It has been recently discovered that its nervous system is very highly developed, consisting of many ganglia, with connecting and rami fying cords.