78 PRESIDENTIAL ADDRESS — SECTION D. 



harzial dysentery, was the common snail, Planorhis boissyi. In 

 the case of S. hcematobium, the agent of urinary bilharziasis^ 

 four snails were incriminated, namely, Bullinus contortus, B. 

 dyhoivski, B alexandrina and B. innesi^ the infection of the latter 

 being rare. The minute morphology of the stages of the cercariae 

 in the snails was not worked out, but has since been ascertained 

 by Faust and by Porter. One transmitter of *S. hcematobium in 

 South Africa was first experimentally determined in Johannesburg 

 by Dr. J. G. Becker at the Institute for Medical Kesearch, and 

 this was confirmed by Cawston and by Porter. The structure and 

 life- history of these human flukes may now be briefly considered. 



Schistosoma hcematobium in South Africa is transmitted 

 chiefly by Physopsis africana, and occasionally by LimncBa natal- 

 ensis.^" The terminal spined ova pass from the human body with 

 the urine. If they reach water, a ciliated larva or miracidium 

 hatches from each egg and swims about. If Physopsis africana, or 

 more rarely Limncea natalensis, is encountered, the miracidia 

 penetrate the pulmonary cavity of the snail, enter the liver and 

 develop into sporocysts. From the walls of the sporocysts buds 

 arise which develop into bifid-tailed cercariae. The cercaria of 

 S. hcEmatohium has a body about 240^ long by lOOn broad, its- 

 tail is about 200[A long by 45^, broad, the caudal forks being from 

 80^1 to lOO^i long. Both the oral and the ventral 

 sucker or acetabulum are small. Three pairs of mucin 

 glands are present, each capped by a hollow, piercing 

 spine, and opening on the outer margin of the oral sucker. A 

 group of several large germ cells lies behind the posterior sucker. 



The cercariae eventually leave the snail and swim about 

 freely. Should they come in contact with the skin of a person 

 bathing or paddUng in the water, or even drinking it, they attach 

 themselves by their suckers to the skin and bore through it, 

 dropping their tails as they do so. They reach the blood vessels 

 and ultimately find their way to the liver and mesentery of the 

 human host, in the blood vessels of which sexual maturity is 

 attained. The adult worms in many cases make their way to 

 the bladder, in the veins of which oviposition occurs. 



The adult S. hmmatobiiim- are unisexual, the males being broader 

 and thicker but shorter than the females. The males that T have obtained 

 experimentally have varied from 3mm. to 17mm. in length. The suckers 

 are near one another, the central one being the larger and being peduncu- 

 lated. The surface of the body is beset with cuticular spines. The 

 oesophagus passes into the intestine which bifurcates behind the posterior 

 sucker. The cwcal forks reunite far back, and the gut ends as a single 

 canal of short length. There are four large, rounded testes. The edges 

 of the body are folded to form the characteristic gynfecophoric canal. 

 The females obtained experimentally by me varied from 5mm. to 30mm. 

 long. They were threadlike, with weak suckers. In each the ovary is 

 in the posterior half of the body, the uterus is voluminous and usually 

 contains a number of mature terminal spined eggs at one time. The 

 vitellaria lie in the posterior quarter of the body. The female is carried 

 in the gynaecorphoric canal of the male. The eggs are deposited in the 

 walls of the bladder, whence they make their way to the cavity of the- 

 bladder and pass out with the urine. 



* Medical Journal of South Africa, xv, pp. 128—133. 



