Page:The American Cyclopædia (1879) Volume VI.djvu/681

ENTOZOA come sickly and are expelled, and not because they are generated by such food of itself; for it must take a long time for them to reach maturity, and they are seldom seen before this age. All attempts to produce these worms in the lower animals by administering eggs have thus far failed. The oxyuris or ascaris vermicularis, the thread or pin worm of the rectum, is the smallest of the human in- testinal worms, the male being about two lines and the female five lines long. FIG. 11. Oxyurisver- micularis (female). 1. Natural size. 2. Magnified. FIG. 12. Trichina spiralis. Jj tai ft Its structure resembles that of its larger rela- tive, and its head is also three-lobed, faintly marked. The muscles of man are sometimes found after death to present a sanded appear- ance, which is caused by the presence of in- numerable little cysts scattered throughout their substance ; these are generally isolated, but in immediate contiguity. These minute bodies when examined microscopically are found to contain immature worms coiled up in the nar- west compass. They are cylindrical and tapering, ^V of an inch long by ^ of an inch thick, and their name is trichina spiralis. Both in the hog and in the human subject they are sometimes found in great abundance in the muscular tissue, sometimes as many as 70,000 or 80,000 to the cubic inch. When first dis- covered in 1832, and for many years afterward, they were supposed to be harmless, no symp- toms connected with their presence having been detected. It is now known that in the cases first observed the parasites had long lain quiescent in the muscular tissue, and that their recent introduction into the system forms one of the most dangerous affections to which the human race is liable. The true physiological history of trichina spiralis is as follows : When the muscular flesh of pork containing the en- cysted parasite is eaten in an uncooked or im- perfectly cooked condition, the cysts are digested and destroyed in the stomach, but the worms themselves, retaining their vitality, pass into the small intestine. In this situation they lose their spiral form, and begin to increase in size ; and by the fourth or fifth day they arrive at ma- turity, attaining a length of from | to f of an inch. At the same time the sexual organs are fully developed, copulation takes place, and the females become filled with mature eggs and embryos, which last are produced alive and in great abundance. These embryos, which are of minute size but in form similar to their parents, then begin to penetrate the walls of the intestine and to dispose themselves over the body. This causes at first an irritation of the intestine, which is usually the earliest symp- tom of the attack. Within a fortnight after the commencement of the symptoms the em- bryos are usually to be found scattered through- out the body and limbs, in the tissue of the voluntary muscles. They are still not more than yfg- or -fa of an inch long. They soon become enclosed in distinct cysts, where they grow to the size of -fa of an inch, and at the same time become coiled up in the spiral form. This period of the invasion of the muscular tissue by the parasite is one of great danger to the patient, being characterized by swelling and tenderness of the limbs, pain on motion, and general fever of a typhoid character. The attack is often fatal about the fourth week. If the patient survive that period, the trichinaa become quiescent, cease their growth, and may remain without further development or altera- tion for an indefinite period. The only pro- tection from danger of being infected with trichina from eating pork is to be sure that the meat is always thoroughly cooked throughout. Tricocephalus dispar (fig. 13) is a nematoid worm which is found, rather rarely and in small numbers, in the cavity of the human caecum, and exceptionally in the colon or in the small intestine. Its anterior or cephalic extremity is slender and filamentous, while its posterior por- tion is thicker and more robust. The male, when extended, is about 1 J D - long; tn female li to 2 in. The eggs are ovoM in form, -^-^ of an inch in length, and marked at each extremity by a minute nipple-like projection. They are discharged into the cavity of the intestine, and the embryo is developed only after a consider- able time, This worm is not known to give rise to any disagreeable symptoms. One more of the human entozoa is sufficiently interest- ing to be mentioned here at length, viz. : the