Bilharziasis 
66 
From these observations we are led to believe that these towns act as foci 
in the distribution of bilharziasis to other parts of Egypt. 
It would seem possible to greatly minimize the spread of the disease by 
attaching some kind of mechanical device, such as a wire gauze filtering appa¬ 
ratus, to the lock gates so as to intercept the masses of floating weeds with the 
contained snails which could then be thrown on to the banks and destroyed. 
At any rate it would capture many mature and infested snails and thus 
materially lessen the number capable of carrying the infection. 
There is one point as regards the prophylaxis which requires explanation 
and that is why S. haematobium infestations occur so commonly in Egypt, 
while at the same time it is so difficult to find Bullinus infested in any 
numbers. During the course of routine snail dissections this has been a con¬ 
stant source of speculation. 
The highest percentage of infested Bullinus we have recorded for one month 
is 9 per cent.— more commonly it is 1 per cent., or even less; in the same locality 
the average infestation rate for Planorbis with cercariae of S. mansoni was 18 
per cent., and occasionally reached as high as 54 per cent. 
Taking all the year round the mansoni infestations in snails were nine times 
commoner than haematobium and add to this the fact that Bullinus is much 
the rarer snail of the two. There is therefore enough scope for further enquiry 
into this most puzzling aspect of this subject. It may be that there are other 
more efficient intermediary hosts of S. haematobium. 
It is important to prevent the entry of infested snails into storage tanks. 
This can easily be done by guarding the intake with a covering of fine-meshed 
wire, but it is insufficient to prevent the entry of the minute newly hatched 
mollusc. 
Such tanks utilized in the canal zone during the Egyptian campaign soon 
became infested with multitudes of Bullinus which passed through the gauze- 
covered intake from the sweet-water canal and which found in this situation 
a suitable habitat. 
Observations showed that snails do not become infested with cercariae till 
they have reached maturity, that is about the third month, so that there is no 
danger to be apprehended from such a circumstance, provided that the tanks 
are frequently cleansed and that necessary measures are taken to guard 
against any faecal or urinary contamination. Of course their presence in 
drinking water constitutes a potential danger and is therefore undesirable. 
It is already known that in Western Australia certain cases of vesical 
bilharziasis occurred after the South African war in persons who had never 
travelled outside Australia. It follows therefore that some Australian molluscs 
must be capable of acting as intermediate hosts for S. haematobium at least. 
Under laboratory conditions, the determination of the infectivity of 
Australian molluscs for both S. haematobium and S. mansoni, the identification 
of those species capable of artificial infestation, and the investigation of their 
life-history, habits, and geographical distribution, are all problems which 
