LIFE HISTORY OF SCHISTOSOMA 215 



people. Recent experiments by Fairley seem to corroborate this 

 view. It is reported that of 625 British soldiers who became 

 infected with blood flukes in South Africa during the Boer war, 

 359 were still on the sick list in 1914 exclusive of those perma- 

 nently pensioned. The cost to the British government for per- 

 manent and " conditional " pensions for these soldiers amounted 

 to nearly $54,000 a year. 



The life history of Schistosoma hcematobium has only recently 

 been worked out by Leiper, of the British Army Medical Corps, 

 in Egypt. It was long known that a ciliated embryo or mira- 

 cidium developed inside the egg shells, even before they left the 

 body of the host, and that these embryos hatched out and swam 



B 



FIG. 66. Egyptian snails which serve as intermediate hosts for blood flukes; A, 

 Bullinus contortus, an intermediate host for Schistosoma hcematobium; B, Planorbis 

 boissyi, an intermediate host for Schistosoma mansoni. (After Leiper.) 



about when the eggs were immersed in water, but beyoud this 

 point the life history could only be conjectured from analogy with 

 the liver fluke. Leiper, who had already made some investi- 

 gations in regard to the life history of S. japonicum in China, 

 worked on the life history of this species, chiefly at El Marg, 

 near Cairo, Egypt. He found that Schistosoma embryos are 

 attracted by several species of fresh-water snails and that they 

 penetrate the bodies of three species, Bullinus contortus (Fig. 

 66 A), B. dybowskii and Planorbis boissyi (Fig. 66B). Here they 

 undergo transformation into sporocysts, from which daugh- 

 ter sporocysts bud off (Fig. 67). After leaving the mother cyst 

 the daughter sporocysts migrate into the tissue of the liver and 

 grow rapidly. They become greatly elongated and eventually 

 ramify throughout the organ, so increasing its bulk and color 

 that an infected snail can be detected at a glance. The sporo- 



