58 
Bilharziasis 
An analysis of Table VI (attached) affords a remarkable proof of Leiper’s 
work in demonstrating the specific relation of the two types of Schistoso- 
midae and their intermediary hosts. 
A description of the following bathing sites well illustrates the variable 
modes in which infection may occur. 
1. At Tel-el-Kebir the troops bathed in a pool formed by the expansion 
of a narrow sweet-water canal (PL V, fig. 2). 
2. At Abou Soueir they became infested by swimming in a much wider and 
deeper sweet-water canal. 
3. At Serapeum they became infested by washing in a shower bath under 
an overflow pipe which conveyed water from the adjacent sweet-water canal. 
(1) Pool at Tel-el-Kebir (PL V, fig. 2). Close to the Rifle Range at Tel-el- 
Kebir and running on the edge of the cultivated land between it and the desert, 
is a fresh-water irrigation canal not more than eight feet across at its widest, 
nor more than three feet deep at any part. There is a clump of shady fir trees 
near the Rifle Range Road, and at this point is a small sluice gate, beyond 
which the canal widens out into the pool in question. It is about 60 feet long 
and 30 feet wide by four feet deep. Beyond this the canal runs on again, 
lined at this point with reeds and rushes. After a morning’s musketry, it was 
a common practice for the troops to have lunch under these trees, and many 
bathed in the pool, while others drank the canal water. In this way the disease 
was contracted. 
On investigating this bathing pool and the canal, we found many snails 
of the species Planorbis boissyi floating down stream, attached to debris or 
ioined together in masses to form rafts. It was the predominant snail of the 
mulluscan fauna of this area. Examination of the submerged rushes and the 
stems of the water-grasses brought to light Bullinus snails in quite large numbers. 
A collection of snails of both kinds was made and on dissection, the cercariae, 
in one case of S. haematobium, and in the other of S. mansoni, were easily 
demonstrated. Thus, out of 513 snails of the species Planorbis boissyi five, or 
1 per cent, were found to be infested, while of 190 specimens of Bullinus two, 
or 1 per cent, (approximately) were found to be in a similar condition. 
The water level of this pool was found to vary on different days, as did also 
the molluscan fauna it contained. From this it was evident that its potentiality 
as a source of infection could vary within wide limits in quite a short space 
of time. In some such manner we may account for the fact that while the great 
majority of cases became infested with both species, a few acquired only 
S. mansoni and fewer still S. haematobium alone. 
A point of great interest was the rapidity and comparative ease with which 
many of these molluscs, particularly Planorbis boissyi, travelled over quite 
wide areas by adhering to floating debris. It seems probable from this that 
snails originallv infested from human excreta in the densely populated regions 
like Zag-a-zig, and perhaps even the environs of Cairo itself, through which the 
' ' -LL-. 
