220 
THOMPSON YATES LABORATORIES REPORT 
By plotting down to scale the figures of the last table, with ages as abscissae, 
and percentages of children infected as ordinates, a curve is obtained shewing the 
relation of age to infection. This demonstrates that the number infected is greatest 
between the ages one and three, and is large also up to five years. The curve shows 
a very decided fall in the sixth year, after which there is a slight rise, and a rapid fall 
again during the ninth and tenth years. As to the reasons for the fall in the sixth 
year, nothing can be given — it may be only accidental. 
(Chart III) 
The curve also shews how immunity from malarial fever is acquired among 
the natives. There is besides a certain inherited immunity, since it is well-known 
that the children of Europeans are severely, and often fatally, attacked by the disease 
in the tropics, while the native children seem to be but little affected. A temperature 
of 103 0 F. was once noted in a child of six months, and occasionally small children 
in arms were met who evidently were sick and had temperatures — but beyond these, 
most of the children seem to suffer but little inconvenience, although an examination 
of their blood at the time might reveal numerous parasites in every field of the micro- 
scope. Immunity appears to be more or less completely established by the time the 
age of ten years is reached, in some cases, however, a longer period appears necessary. 
This acquired immunity lasts for a considerable number of years, in many 
cases a life-time — the period really depending on the extent and frequency of infection 
during childhood and on individual idiocyncrasy. It has been observed that in all 
the places visited by us a proportion of the native children were infected, and that 
the proportion varied and, therefore, the chances of exposure to infection varied. It 
is possible that there exist in West Africa towns and villages where no malarial 
fever exists — the natives of such places on entering a malarious district would suffer 
almost as severely as Europeans. It was only occasionally that we met a native adult 
complaining of fever, and then only slight inconvenience was occasioned by the attack, 
which seldom lasted more than twenty-four hours. The returns of the Principal 
Medical Officer for Southern Nigeria shew a number of adult natives treated, entered 
as suffering from malarial fever. As microscopical examination was but very little 
used as a means of diagnosis, it is probable that, although some of these cases may 
have been true malarial fever, others are, no doubt, fevers of a different nature. In 
two cases of adults suffering from fever, examined by us, ring forms were found in 
fair number. 
The actual extent and nature of the infection in individual cases at the time of 
examination are given below. 
It will be seen that aestivo-autumnal, quartan, and tertian parasites were found, 
and, at the time of our visit, the majority of the cases were aestivo-autumnal, while 
there were also a number of quartan cases, and only a few tertian. Probably the 
