SCHISTOSOMUM MANSONI 



589 



dominates in the pelvic veins; (6) 5. mansoni gives rise to an illness likekata- 

 yama disease, and never to the bladder symptoms produced by 5. hcsmatobium; 

 (7) the morbid anatomy of cases invaded by S. mansoni agrees with those 

 invaded by S. japonicum, and differs considerably from those caused by S. 

 hcBmatobium ; (8) the geographical distribution is in opposition to Looss's 

 view that the lateral-spine d eggs are unfertilized because they are the only 

 eggs found in Brazil, the Antilles, and Surinam. 



He also found a single type of egg with lateral spine in the uterus and 

 ootype of sixty females. 



In 1915 Leiper's work in Egypt proved that the miracidium 

 developed in a special snail, Planorbis boisseyi, and that the 

 vertebrate could be infected by the skin or oral mucosa. 



In 1917 Chalmers and Pekkola 

 in the Anglo-Egyptian Sudan 

 have experimentally infected the 

 same snail with the miracidia, 

 and obtained cercariae, and in 

 the same year Lutz carried out 

 similar experiments in Brazil 

 with P. olivaceus. 



In 1917 Iturbe, working in 

 Caracas, Venezuela, found that 

 the miracidia could infect Pla- 

 norbis cultratus and P. guadehi- 

 pensis, but the latter was more 

 easily infected, and showed 

 typical cercarise by the end of 

 the sixth week. He considers it 

 to be the true carrier of the in- 

 fection there. He noted that it 

 was easier to infect animals per 



000 



Fig. 230. — Outlines of the Eggs 

 OF (i) S. japonicum (without 

 spine); (2) 5. hcBmatohium; (3) 

 5. mansoni. (After Sambon.) 



OS than by the skin. He found no less than 120 out of 400 

 specimens of P. guadelupensis to be naturally infected around 

 Caracas. The ' rediac ' described by him have since been recognized 

 as immature stages of a new species of Tetracotyle. 

 Morphology. — ^Sufficiently described above. 



Life-History. — -The adults live chiefly in the mesenteric veins, 

 and the ova pass into the submucosa of the large bowel, and through 

 this into the faeces, and so escape from the body. The egg is 

 oval, 112-162 X 60-70 microns, and possesses a well-defined lateral 

 spine. 



Fig. 231, — Schistosoma mansoni. 

 (After Holcomb.) 

 a, Male; h, egg; c, larva. 



