PRESIDENTIAL ADDRESS — SECTION D. 79 



ScJiistosoma mansoiii, the excitant of billiarzial dysentery, i& 

 transmitted in South Africa — as I* have shown experimentally — 

 by at least three molluscs, namely, Planorbis pfeifferi, Pliysopsis 

 africana and Isidora tropica. Schistosoma niansoni 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 collected 

 in Natal. Planorbis pfeifferi, in my opinion, is probably the most 

 common transmitter of S. niansoni and Isidora tropica the least 

 common. In South America, Iturbe and Gonzalez have proved 

 that Planorbis guadaloupensis is the commonest molluscan host 

 for the fluke. 



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

 as that of S. hceniatobiuni. The ova are lateral spined. The- 

 miracidia are liberated in water and if successful in reaching one 

 of the molluscs mentioned, sporocysts and then cercariae are 

 produced. These cercarife are smaller than those of S. 

 luematobium, the body of each being about 150[x long and 60^ 

 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. The rudiments of 

 the genitalia consist of numerous small cells. The cercariae leave 

 the snail and penetrate the skin of persons exposed to the water 

 containing them as in the case of S. hceniatobium. 



The adult male differs from that of iS'. hamatobiiim in that it has 

 eight small testes, while its alimentary canal has forks that unite after a 

 relatively short distance, the single portion of the intestine hence being 

 long. The males that I have obtained experimentally were from 3mm. 

 to 11 mm. long, while the filiform females were from 4mm. to 14mm. long. 

 In the female 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 females migrate, and cause ulceration there. The 

 eggs pass out of the faeces of the infected persons. The dysentery pro- 

 duced is of a very intractable type. 



Preventive measures against infection with Schistosoma 

 hcBm.atobium and S. viansoni may be briefly summarised. 

 Measures against pollution of soil, and especially of water, by 

 urine and faeces of infected persons must be instituted — proper- 

 disposal of excrement, preferably by incineration, is necessary. 

 Great care is needed to prevent water contamination and infection 

 of water-snails. The destruction or reduction of the molluscan 

 population can be brought about to a large extent by the intro- 

 duction of domesticated ducks. As the cercariae die after a period 

 of about two days, allowing water to stand for at least two days 

 before use will permit of the death of the cercariae. Dr. Cawston 

 has found that small fish of the " millions " type will feed on 

 cercariae as well as on mosquito larvae, and hence serve a dual 

 purpose in sheets of water into which they have been introduced. 



The successful treatment of bilharziasis by intravenous injec- 

 tions of tartar emetic was first set forth by Dr. J. R.- 



* Medical Journal of South Africa, xvi, pp. 75 — 76. 



