292 



DISEASES OF THE LIVER. 



excrements, and are scattered on the ground, either smgly or confined 

 in the escaping segments of the tapeworm. Once ujjon the ground, 

 they are easily washed along by rain into the 

 drinking water, j^onds, or brooks, or scattered on 

 the grass. Upon being swallowed with fodder or 

 water, they arrive in the stomach of the inter- 

 mediate host (cattle, sheep, etc.), where the egg- 

 shells are destroyed and the embryos set free. 

 The embryos then traverse the intestinal wall, 

 and, according to most authors, arrive either ac- 

 tively, by crawling, or passively, by being carried 

 along l)y the blood, in the liver or lungs, where 

 they undergo certain transformations in structure. 

 While still in the finer branches of the blood- 

 vessels of the liver, which they transform into 

 small, irregularly-shajjed tubes about 12 to 15 mm. 

 long and 1 to 1"5 mm. broad, the embryos lose their six hooks, and 

 develop into small, round kernels, which are generally situated at one 



Fig. 139.— Egg of the 

 uiarginate tapeworm 

 ( Tfenia niargiitata), 

 with six-hooked em- 

 bryo, greatly magni- 

 fied. (Stiles, Annual 

 Eeport U.S. A. Bureau 

 of Agriculture, 1901.) 



Fig. 140. — Portion of the liver of a lamb which died nine days after feeding with eggs 

 of the marginate tapeworm [Ttenia marijinata), with numerous "scars," due to 

 young parasites. (After Curtice.) 



end of the tubes. The embryo can first be seen about four days after 

 infection. The " scars " (Figs. 140 and 141) described in the liver of 



