88 
Bilharziasis 
FURTHER EXPERIMENTS IN NATAL. 
In the spring of 1916, I made an exhaustive study of the commoner fresh¬ 
water snails of Natal. I examined, microscopically, the livers of 1500 specimens. 
They included seven different species of snail. I could find no Bilharzia 
cercariae in any species of snail except in Physopsis africana. I examined 
250 Planorbinae. It is interesting to note that Schisiosomum mansoni which 
has this species of snail in Egypt as its intermediary host is unknown in Natal. 
I encountered three different forms of Bilharzia cercariae in the specimens of 
Physopsis africana which I examined, one was an eye-spotted form, for which 
I have suggested the name of Cercaria bilharziella lunata, in view of the 
crescentic form of its eye-spots. Another, for which I have suggested the 
name of Cercaria secobii, has very long prongs to its divided tail; the third 
form corresponds to that which causes Schistosomiasis in Egypt and the 
Far East. In one bathing-place which is known to be a source of Bilharziasis, 
I found 14 % of the specimens of Physopsis africana infected with this human 
form of cercaria. In the April number of the Medical Journal of South Africa, 
Dr J. Gr. Becker reported that he had found similar cercariae in three out of 
13 specimens of this same snail which he had collected from an infected 
bathing-pool at Nijlstroom in the Transvaal. 
I then undertook experiments to infect with miracidia, obtained from the 
urine of Bilharzia patients, a number of this species of snail. 
On April 22, I found that 14 out of 31 specimens, obtained from the 
Umsindusi river, which I had exposed to infection by miracidia three weeks 
previously, contained Bilharzia cercariae— i.e. 45%. Examination of 197 
specimens direct from the river showed an infection of only 15 %. 
During May, when 22 % of the specimens in the river were infested with 
Bilharzia forms, the percentage of infected snails amongst 19 which had been 
exposed to infection by miracidia 36 days previously was 37 %. 
On June 9th, 60 specimens from the Umsindusi which had been exposed 
to infection on May 20 were examined for cercariae. Sixteen contained 
Bilharzia forms. Of 30 specimens from the same source, which had been kept* 
for three weeks in clean water, seven were infected. 
Similar experiments with Planorbinae and Limnaea proved entirely 
negative. 
Whilst these experiments were in progress, I attempted to produce 
Bilharzia infection in 12 white rats, six guinea-pigs and six pigeons. During 
1915, Dr E. Warren had undertaken similar experiments, submitting rabbits 
and mice to hypodermic infection with Bilharzia cercariae, but with negative 
results. 
In my experiments, I immersed rats and guinea-pigs for an hour on several 
days in water swarming with Bilharzia cercariae; to others, I gave water 
containing cercariae by the mouth or rectum. No symptoms were produced at 
the end of three months and no parasitic worms were discovered post-mortem. 
