20 —

Irrigated Area. Bilharzia Snails Increase. The rapid increase in the bilharzia snail population during the last two years is very striking. In the autumn of 1926. the irrigation system had been working for over a year, and at

that time bilharzia snails could only be found in six of the canals. They are now present in large numbers in every canal of the system. Three new blocks in the north of the area were not irrigated until August last, and yet both the bullinue and planorbis varieties were found in these canals in November.

Varieties. Both kinds of snail are now found. In 1927 the planorbis variety was found in two blocks only (Barakat and Tayiba, the two oldest blocks). This variety is now found in twenty blocks.

The snails found in the canals and sent to the Wellcome Tropical Research Laboratories for identification have been indentified as follows :—

Bullinus

Planorbis

Innesii Contortus

Dybowski Boissvii

K/ Alexandrinus Pfeifferi

* in order of frequency.

* in order of frequency.

Snails infected with bilharzia cercaria have been found in Tayiba, Barakat, Suriba and Medina canals. It is probable that several other canals contain infected bilharzia snails. To meet this state of affairs the snails in all the distrib¬ utary canals will be systematically destroyed during the non-watering season, either by completely drying out the canals or by partially drying out the canals, and treating the residual water with Sizolin.

This is done, not with the purpose of diminishing the snail population, as the dried out canals, very soon after they have been refilled from the main canal, are again infested with mature snails, but with the intention of killing all the infected snails, and starting again with canals infested, but not infected.

Destruction of snails during the non-watering season 1928. All irrigation ceases between April 15th and July 15th but water has to be run in the main canals and in something like half of the distributary canals to ensure a supply of water for the houses and gardens of the Syndicate Inspectors, and for the native population and their animals. 1,185 kilometres of distributary canals had to be dealt with. 376 kilometres had to be treated with Sizolin, the remainder were dried off in rotation.

In spite of this systematic destruction, the four canals referred to above were found to contain infected snails. Either these snails must have been reinfected between August and the end of the year, or else owing to some lack of co-operation between the sanitary authorities and the water controllers, water was re¬ admitted to these canals before the snails were completely dead. If this latter were the case it remains to be seen if the snail destruction can be made more final and more universal in the coming year.

Bilharzia infection of children in the irrigated area. During the 1926 survey of human bilharzia infection m the irrigated area, locally infected children were found in the villages in the following blocks :—

Hosh . . . . . . . . .. . . 7 Hamad-el-Nil . . . . . . . . . . 3 Komor and Radma . . . . .. .. 3 Tayiba . . . . . . . . .. .. 8

Barakat .. .. .. .. .. .. 15 Abdel Rahman . . . . . . . . .. 1