2IO 
THOMPSON YATES LABORATORIES REPORT 
them, where they swell out into shallow pools with sluggish stream, form excellent 
breeding-places, and probably in the dry season, when they almost dry up, the pools 
last remaining perform a similar function. By wading along the course of some of 
these streams we are able to locate the breeding-places of Anopheles which they provided, 
always at a distance not exceeding two or three hundred yards from human 
habitations. Beyond this distance above the district of huts and bungalows we found 
no larvae. 
Still another condition was observed at Lokoja. At a point near the river 
bank we found a small area of cultivated land. We were unable to ascertain precisely 
the nature of the produce, but it was probably rice. The surface was dug so 
as to form rows of butts and furrows. One portion of the area was swampy, and 
water puddles were formed for a short distance along many of the furrows, and also 
along a narrow footpath crossing the field. In many of these puddles Anopheles 
larvae were found. Habitations in the immediate neighbourhood were scarce, but at 
a distance of two hundred yards was a collection of native huts. 
Statistics. — Northern Nigeria. — The only statistics available are those given in 
the reports of the medical officers of the West African Frontier Force. 
(Chart II) 
The points of the line curve represent the percentages per month of the total 
European force admitted into hospital. Those of the dotted curve shew the actual 
number of cases admitted per month. Both curves shew a marked increase in the 
number of cases of malarial fever after the beginning of the rainy season, and the 
former also a smaller increase after the cessation of the rains. During the course of 
the wet season itself the breeding-places of Anopheles would be continually flooded out, 
but during its onset and cessation the insects would be able to breed continuously. 
