DISEASES OF SWINE 535 



recommended in peritonitis and pleurisy. The larvae of the Taenia 

 marginata is not of as much economic importance as the larvae of 

 the Taenia solium. It does not cause as serious a line of symptoms 

 in its host as the cysticercus, and does not infect man. (Ind. B. 

 100.) 



TRICHINOSIS. 



Trichinosis is a disease occurring in man and other animals as 

 a result of eating flesh containing the living larvae of a parasite, 

 Trichinella spiralis, commonly known as trichinae. 



These larvae have been found encysted in the muscles of many 

 different kinds of mammals, most frequently those of omnivorous 

 or carnivorous habits. The occurrence of trichinae in herbivorous 

 mammals, or in those which do not normally eat meat, is very rare, 

 and results only when, abandoning their usual food habits, or acci- 

 dentally, these animals eat meat wnich happens to be infested with 

 the parasite, or when as a matter of experiment they are purposely 

 fed such meat. From the standpoint of public health, the only 

 animals which are of importance in this country as sources of infec- 

 tion and propagators of the disease are hogs and rats. Man becomes 

 infected through eating trichinous pork, hogs become trichinous by 

 eating the trichinous flesh of other hogs or of rats, and rats acquire 

 the parasite by eating the flesh of trichinous hogs or by eating other 

 rats which happen to be infested. The country slaughterhouses 

 where hogs are commonly kept and fed on the offal of slaughtered 

 animals and where rats usually abound are one of the most impor- 

 tant factors, if not the most important, in the propagation of infec- 

 tion. 



Life History and Description. Three stages may be dis- 

 tinguished in the life history of the parasite the adult, the em- 

 bryo, and the encysted larva. 



In the adult stage the parasites are small, slender worms, grad- 

 ually increasing in thickness toward the posterior end, and scarcely 

 visible to the naked eye. This stage of the parasite lives in the in- 

 testine and develops from larvae swallowed in infested meat. The 

 cysts surrounding the larvae are destroyed by the action of the gas- 

 tric juices, and the larvae, passing from the stomach into the intes- 

 tine, grow to maturity in about two days, and, according to their 

 sex, become adult males or females. The male is the smaller 

 of the two, measuring only about 1.5 mm. in length (about 1-16 of 

 an inch), the female measuring 3 to 4 mm. in length (about 1-8 to 

 1-6 of an inch.) 



Apart from differences in their internal anatomy, the two 

 sexes may be distinguished by the presence of a pair of conical pro- 

 tuberances at the posterior end of the male, which are lacking in 

 the female. Copulation occurs between the two sexes, and the fer- 

 tilized eggs in the female develop into embryos, which finally escape 

 from the uterus through an opening on the ventral surface located 

 some distance in front of the middle of the body. At birth the 

 embryos are elongated and wormlike, measuring in thickness near 



