TRICHINOSIS — SCHWARTZ 417 



attain a length of 1.5 mm. (about i/ie of an inch), tend to pass out 

 of the intestine shortly after their reproductive functions have been 

 completed. However, adult worms of both sexes may persist in the 

 intestine for several weeks. 



The fertilized eggs develop within the uterus of the mother worm, 

 and the larvae begin leaving the maternal uterus 4 to 5 days after 

 the mating of the sexes, or 6 to 7 days after the ingestion of trichin- 

 ous meat by a susceptible host. While the birth of young worms 

 may continue for several weeks, most larvae are apparently dis- 

 charged by the adult females during the first 2 weeks of their fertile 

 period. 



The new-born larvae, 0.1 mm. (about 1/250 of an inch) long, are 

 deposited in the lymph spaces through the vaginal aperture of the 

 female trichina, this aperture being located in the anterior part of 

 the worm. The larvae are carried by the lymph to the thoracic duct, 

 thence through the venous system into the heart, and finally into the 

 arterial circulation. Those larvae which are carried to the striated 

 muscles leave the capillaries and penetrate into the primary muscle 

 bundles. The muscle fibers become most heavily invaded 9 to 10 days 

 after infection, or 3 to 4 days after the birth of the young worms 

 lias begun. Within 10 to 14 days after their penetration into the 

 muscles, the larvae have attained their maximum length, which is 

 10 times their original length; each larva rolls itself into a spiral 

 and becomes enclosed in a capsule. 



While the origin of the capsule is still a somewhat debatable point, 

 it is certain that the presence of the parasites in the muscle fibers 

 stimulates the formation of connective tissue around each worm; 

 sometimes, however, two, and more rarely more than two, worms are 

 enclosed in a single capsule. Capsule formation begins about 1 

 month after infection, and a thin-walled capsule is readily recogniz- 

 able about 6 weeks after infection. Sooner or later, but not earlier 

 than 6 months after infection, as a rule, the capsules begin to calcify, 

 calcium being deposited at first at the poles, the entire process of 

 calcification requiring about li/^ years. This accounts for the failure 

 to find the white, oval cysts in infested pork, since most hogs that 

 come to slaughter in this country are approximately 6 to 10 months 

 old. In the experience of the author of this paper, only one speci- 

 men, among the numerous samples of pork examined for trichinae 

 in the laboratory of the Zoological Division and elsewhere, contained 

 calcified cysts, visible to the naked eye as small, oval, chalky spots, 

 such as were observed and described by Leidy in 1846 (1) . The larvae 

 may remain alive in the calcified cysts for a number of years. Sooner 

 or later, however, the larvae die and become absorbed, or undergo 

 calcification and break down into crumbled masses. 



