Distribution of Tropical Diseases in Africa. 423 
have personally noticed the same characteristics north of the 
equator. 
Again, the religion and customs of the inhabitants neces- 
sarily influence their susceptibility to disease, or their power 
of recovery after having been attacked by disease. There is 
a marked difference between the stolid, fatalistic, Moham- 
medan and the superstitious pagan. A difference also 
obtains in many districts owing to diet, partly influenced it 
is true by custom, but also by religion, and the vegeta- 
rians and mixed feeders are liable to definite varieties of 
disease. 
Although it is a mistaken notion that insanity and nervous 
diseases do not obtain among the natives, yet they are 
undoubtedly less frequent in Africa than they are in 
temperate latitudes; and it is certain that civilisation, or, at 
any rate, contact with the whites, has a more or less deterio- 
rating effect upon the native population. 
It is now necessary to refer briefly to the subject of 
acclimatisation, and to endeavour to answer the question 
which is frequently put —Can Europeans become acclimatised 
in Tropical Africa ? 
My strong opinion is that it can only be possible if migra- 
tion occurs step by step, and in estimating the possibilities 
of acclimatisation we must count by generations rather than 
by years. I believe, however, that our increased knowledge 
of climatology and hygiene renders the problem of acclimatisa- 
tion easier than it was, and, given picked individuals and the 
careful selection of tropical areas in which to colonise, I see 
no reason why, with precautions, inhabitants of the temperate 
zone should not colonise even in Central Africa. In the 
selection of emigrants, great care should undoubtedly be 
taken, and all persons with a tendency to gout or 
rheumatism, diabetes or albuminuria, those with a nervous 
or alcoholic family history, or those suffering from either 
acquired or hereditary syphilis, should certainly be restrained 
from emigrating to Tropical Africa. 
As I before indicated, environment definitely influences not 
only individuals but nations, and for- this reason a marked 
difference obtains between the adaptability of residents 
