90 
PROPHYLAXIS OF MALARIA. 
malarial infections results in the production of carriers of the disease 
and that many patients discharged as cured from the hospital will 
he found to have plasmodia in their blood for long periods before a 
relapse occurs, and that many of these become efficient “ carriers ” 
of the disease owing to the development of gametes during these 
latent periods. 
Proportion of latent infections .—The proportion of latent infec¬ 
tions varies greatly in different localities as is shown by the tables 
that follow, but it may be stated that such infections occur in a 
considerable percentage of both children and adults in every region 
in which malaria is endemic to any extent, and that the discovery 
and treatment of these infections is of great importance in the pro¬ 
phylaxis of malaria in such regions. In the following tables the 
percentage of malaria in the cases recorded was determined by the 
finding of the plasmodia in the blood, which is a much more accurate 
method than the splenic index which will be discussed later. 
Koch, 45 to whom we owe practically the first observations along 
this line, concluded, from his work in Africa, that latent malarial 
infections were almost entirely confined to children, but further ob¬ 
servations have shown that latent infection is very frequent in 
adults in malarial localities, and that the true index of the prevalence 
of the disease in any region can only be determined by the examina¬ 
tion of the blood of both children and adults. The following tables 
give the results of the principal investigations in regard to the pre¬ 
valence of latent infections in the natives of malarial regions: 
Table I.— Thomas's observations in Manos, Xorth Brazil. 
Age. 
Number 
examined. 
Number 
infected. 
Percent¬ 
age. 
6 months to 2 years. 
9 
38 
51 
59 
3 
20 
28 
27 
33.3 
52.6 
54.9 
45.7 
2 years to 5 years. 
5 years to 8 years. 
8 years to 10 years. 
157 
78 
49.6 
Total. ^ . 
James, 47 in India, found the percentage of latent infection in 
native children to vary greatly in different localities. At Mian 
Mir children up to 2 years of age showed 80 per cent infected; up 
to 5 years, 66 per cent; up to 10 years, 50 per cent, while children 
older than 10 years showed no infection. At Ennur children up to 
3 years }^ears of age showed 65 per cent infected; up to 5 years, 51 
per cent; up to 10 years, 46 per cent, and up to 15 years, 16 per cent. 
At Camp Stotsenburg, in the Philippine Islands, I 48 have exam¬ 
ined the blood of 45 native adults and 180 native children, all o't 
whom at the time of examination were free from svmptons of mala- 
