14 STUDIES ON NASAL SCHISTOSOMIASIS [Vol. XXIV, Part I,
probably created doubts in the minds of some of the earlier workers, who considered
them as identical with the eggs of S. spindale.
In examining the samples of urine and faeces for the presence of eggs
the ordinary concentration method was followed, which may be briefly described
as follows. The faecal sample was emulsified with normal saline in the proportion
of one to eight roughly. The emulsion was then strained through an ordinary tea-
strainer to remove the coarse debris and the liquid was allowed to stand for about
20 minutes for the eggs to settle down. Usually four preparations from each such
sedimented sample were examined. As regards the samples of urine, they were
just allowed to stand and the sediment was then examined.
Fresh-water molluscs were collected from different localities and tested for
natural infections by (1) the ordinary test-tube method, in which the snails were
kept separately in clean test-tubes containing three-fourth clean water to examine
at subsequent intervals if they were discharging cercariae, and later by (2) dissecting
them out for the developing larval stages, if any. Physical and topographical
features of the area were studied and a close observation was made on the ecology
and distribution of the molluscan intermediaries of the parasite with a view to
correlate them with the incidence and distribution of the disease and also to formulate
the most applicable prophylactic measures.
This programme of work was followed during a tour extending over a period
of about one month, from 24 February to 24 March 1952, in the infected areas,
which were marked off from the records of the State Civil Veterinary Department.
The itinerary was so planned as to visit each district of the endemic zone in turn.
The number of places visited (indicated on the map, Fig. 1) was limited, but this
did not interfere with the object of the survey on account of more or less similar
conditions prevailing over the entire region.
TOPOGRAPHY
The endemic sone of nasal schistosomiasis in Bihar lies between latitudes
25ºN and 25.60'N and longitudes 84ºE and 85.70'E and is marked off from the
surrounding areas by the Main Line of the Eastern Railway (formerly called East
Indian Railway) on the north and the Grand Chord Line of the same Railway on
the south. On the west and the east the boundaries extend respectively to the
areas irrigated by the Buxar canals and the low-lying areas watered by the river
Poonpoon, Phalgu and Sakri with their tributaries. The physical features of the
area seem to be an important factor in the occurrence of the disease, which has a
more or less definite zonal distribution, as indicated in the map showing infected
areas roughly.
Methods of irrigation
The entire region is a flat country in the Gangetic plain and is watered by the
rivers Sone and Ganges with their tributaries and canals. The land slopes down
to the north-east. The Sone has been harnessed by a dam near Dehri from where
two Main Canals have been taken out, one on either side of the river. The Western
Main Canal serves the district of Shahabad and the Eastern one irrigates parts of
Gaya and Patna districts. The Shahabad canal system is more widely spread with
all its distributaries in between the two railway lines named above. The areas of
Piroo and Bikramganj, which were found to harbour the greatest number of cases