158 LIFE-HISTORIES OE TKEMATODES. 



(2) Schistosoma mansoni. 



Schistosoma mansoni, the excitant of bilharzial dysentery, is 

 transmitted in South Africa by at least three molluscs, namely, 

 Planorbis 2)f c iff er i, Physopsis africana, and Isidora tropica. The 

 fluke is not a common parasite of man in the Union of South 

 Africa, but is fairly common in British and Portuguese East Africa 

 and very common in South America. My infected molluscs were 

 obtained in Natal. Planorbis pfeifferi, in my opinion, is probably 

 the more common transmitter of Schistosoma mansoni in South 

 Africa, and Isidora tropica the least common. I have only once 

 so far found Isidora infected with the cercariae of S. mansoni, but 

 was able to produce the adult worms in a white rat exposed to 

 these cercariae. Fuller details are set forth in my article (1920) 

 in the "Medical Journal of South Africa," Vol. XVI, p. 75, 

 already cited. 



The life-history of Schistosoma mansoni is on the same lines 

 as that of S. haematobium. The eggs are lateral spined, and are 

 passed with the faeces of an infected person. On reaching water the 

 miracidia emerge from the eggs, swim about, and should they 

 succeed in reaching one of the afoi'ementioned molluscs, enter the 

 pulmonary cavity and reach the liver where they develop into 

 sporocysts that produce cercariae. These cercariae are smaller 

 than those of S. haematobium, the body of each being only about 

 150/i long and 60 /a broad, the tail being proportionately smaller. 

 The body contains two pairs of large acidophile mucin glands and 

 four pairs of smaller basophile mucin glands. Each gland opens 

 by a hollow spine at the anterior end of the oral sucker. Numerous 

 small cells constitute the rudiments of the genitalia. These 

 cercariae leave the snail and, if they reach the human body, they 

 develop as with S. haematobium in the liver and mesenteric veins 

 and become sexually mature. 



The adult male in general structure resembles that of 

 S. haematobium, but has eight small testes, while its alimentary 

 canal has forks which unite relatively early, so that the single 

 portion of the intestine is long. The males that I have obtained 

 experimentally were from 3mm. to 11mm. long. The filiform 

 females measured from 4mm. to 14mm. long, had very weak 

 suckers, and presented the same structure of the alimentary canal 

 as the male. The ovary is median, the vitellaria occur in the 

 posterior part of the body, and the uterus usually contains one only 

 of the lateral spined ova at a time. The ova are laid singly in 

 the submucosa of the rectum whither the female migrates after 

 fertilisation, and produce ulceration there. They pass out with 

 the stools of the infected person. 



(3) Preventive Measures. 



Preventive measures against infection with Schistosoma 

 haematobium and S. mansoni may be briefly summarised. Measures 

 against pollution of soil and especially of water by urine or faeces 

 of infected persons must be instituted. Proper disposal of excre- 

 ment, preferably by burning, is necessary. Great care is needed 



