MALARIA EXPEDITION TO NIGERIA 207 
details for the construction of the following tables and charts illustrating the relation 
between the amount of rainfall and the prevalence of malarial fever. 
For an estimation of the rainfall we have found it necessary to take the 
average fall of three stations in the colony, and for the number of cases of malarial 
fever we were not able to obtain the reports of all the stations. 
The following table gives the average rainfall per month of three stations in 
Southern Nigeria (one of which is Old Calabar) and the total number of cases 
reported as malarial fever among Europeans. It is necessary to point out that a 
few of the cases among Europeans were probably not truly malarial in character. 
Average Rainfall 
Total Number of 
European Cases 
1899 — April 
10-46 
30 
May 
II7I 
83 
„ June 
H77 
40 
n My 
21-13 
54 
„ August ... 
27-09 
38 
„ September 
19-65 
47 
„ October... 
9-08 
37 
„ November 
10-40 
33 
„ December 
4 - 5 8 
31 
1900 — January 
2-68 
20 
„ February 
8-63 
25 
March 
9H3 
26 
(Chart I) 
It is to be noted how closely the number of cases of malarial fever among 
Europeans follows the variations in the rainfall, and especially how the largest 
number of cases occur at the time when the rainy season has become fairly 
established. Allowing for the period of the life history of the malarial parasite in the 
mosquito, and for an incubation period of the disease in man of from seven to 
twenty days, the relation of cases to rainfall is such as would have been anticipated 
from a consideration of the nature of the breeding places of Anopheles in the districts 
considered. 
