— 40 Malaria. From the observations recorded this would appear to be the most prevalent endemic disease affecting the tribe. The splenic index is as follows :— Males .. .. .. •• .. .. 0.51% Females .. .. .. .. .. 1.11% Children .. .. .. .. .. 30.66% Actual figures are included as these show intimately splenic enlargement is related to topographical conditions.

For example Tonga and Fanyikang divisions are affected by the proximity of the Khor Lolle, Dettim by Khor Harami, and so on.

The index for children though comparatively high is lower than one would expect considering that practically every child apparently passes through one or more attacks of malaria. The youngest child with an enlarged spleen was 13 months old.

Though malaria does occur earlier than this, it would appear to be rare in the first twelve months owing, I presume, to the constant care of mother. (Inciden¬ tally Shilluk women are very good mothers). From that age the numbers rapidly increased to reach an acme from the 5bh to the 6th year after which they showed a fairly even decrease until by the 16th year the index practically approximated that of adult life.

The low index for adults is probably attributable to a certain degree of immunity conferred by previous attacks in childhood. Debilitating conditions whether physiological or pathological would appear to weaken this immunity, hence the higher incidence of the disease in women. Further practically all adults actually suffering from the disease were in a more debilitated condition than one would expect to originate from the actual attack itself.

These observations are borne out to a certain extent by the actual cases of clinical malaria seen which were :— Adult males . . .. .. .. .. .. 16 ,, females .. .. .. .. .. 27 Children . . . . .. .. .. .. 74 These figures are low, but it must be remembered that the trek occurred in the non-malarial time of the year.

Few microscopical examinations of the bloods were made and work in this direction proved rather disappointing. Of 200 slides examined only 10 per cent, were positive. Slides taken from actual cases of clinical malaria in adults were less productive of result than those from children with enlarged spleens only.

This may be attributable to the theory of acquired immunity diminishing the free circulation of the parasites in the blood stream.

In children with enlarged spleens the age most productive of parasites in the blood was 5-6 years, presumably just before any acquired immunity became manifest. It will be noted that this is also the age at which enlarged spleens were most prevalent.

From the examinations made it appears that malignant tertian is the most prevalent parasite except on the Zeraf where quartan parasites only were found.

The latter all occurred in children with enlarged spleens whose ages ranged from one year to ten years. No quartan was found in any other part of the area covered.

Unfortunately time did not permit during this part of the Surve}’ of any investigation of the classification or infectivity of the prevailing mosquitoes. It is hoped that it will be possible to investigate those on the continuation of the survey.