152 
MALARIA 
Wilson Dam area, T. V. A., the peak of 
malaria for whites is in June and for ne¬ 
groes in August. These differences are 
confirmed in the laboratory. Among G. P. 
I. patients, negroes exhibit a high degree 
of tolerance to P. vivax inoculations, which 
is ordinarily absolute for the strains now 
being employed in malaria therapy. This 
tolerance is found in children as well, which 
suggests that it is racial and not acquired. 
In areas where P. falciparum infections 
predominate the matter is not so clear. 
D. B. Wilson (1939) believes that in the 
black population in East Africa, inherited 
tolerance plays little part in the ultimate 
acquisition of immunity, for the babies 
suffer from intense infections, and while 
they rapidly acquire resistance, this is not 
dependent upon race but upon frequency 
of infection. This is supported by van 
Nitzen who says that natives of Ruanda 
when they come to the highly malarious 
mining camps of Katanga, get attacks com¬ 
parable to those of Europeans, with cere¬ 
bral forms and blackwater fever. Accli¬ 
matization takes about 3 years. Neverthe¬ 
less Giglioli (1938c) points out that in Brit¬ 
ish Guiana, negroes and East Indians live 
under exactly the same conditions and are 
equally exposed to malaria. The negroes 
become infected with malaria like the In¬ 
dians and the parasite rates are comparable 
(60 and 74), but the negroes tolerate the 
infection better and react less violently 
with a spleen rate of 13 as compared with 
70 among the Indians. The fact that the 
parasite rates are so nearly equal shows 
that the tolerance is to the effects of the 
parasites and not to the parasites them¬ 
selves, and negro communities, while not 
great sufferers from clinical malaria, may 
serve as continual foci of infection to other 
racial groups. 
8. The influence of sex. Significant dif¬ 
ferences are occasionally reported between 
the sexes. Russell found the parasite rate 
for boys to be 32 and for girls 22 in some 
Indian villages, and I have noted the same 
thing in Sardinia. This is not a constant 
finding, and is usually attributed to differ¬ 
ences in exposure to infection. 
9. The effect of individual and family 
disposition. Clark found in Panama that 
the bulk of the malaria was confined to the 
same individuals or families year after 
year, and Barber and Komp, out of their 
long experience, came to the considered 
opinion that “it is the occasional heavy 
carrier who is most dangerous to a com¬ 
munity.” 
10. The influence of social factors. Ma¬ 
laria has long been classed as a social dis¬ 
ease, and the implication is that economic 
stress reflected in low standards of living, 
undernourishment, lack of medical care, 
overcrowding and so forth, creates a situa¬ 
tion so favorable to the persistence of ma¬ 
laria in the individual and in the group 
that it cannot be eradicated without drastic 
changes in living conditions. Small, sub¬ 
standard aggregations of people living 
under such conditions at the edge of more 
prosperous communities, are seed beds of 
malaria for the general population. Thus 
the negroes in our South, like the gypsies 
in Hungary, are foci of infection which in¬ 
sure a constant supply of gametocytes, but 
whether this is to be attributed to social 
factors or to the fact that these unfortunate 
groups are almost always more accessible to 
mosquitoes than the towns people is not 
clear. The whole question is very contro¬ 
versial and a considerable literature has 
grown up about it (Hackett 1937). 
Social factors may produce a lag in the 
rise or fall of malaria endemicity in a com¬ 
munity, but this has never been measured 
or proved to exist. 
11. The influence of habits and occupa¬ 
tion. It is unnecessary to dwell on the fact 
that some people are more exposed than 
others to infection by reason of their man¬ 
ner of life. In the hill towns near Rome, 
malaria is an occupational disease of the 
farmer who descends daily to the plain 
early in the morning and does not return 
to his hilltop until after the anopheles have 
become active in the evening. 
Summing up, we find that anopheles in 
proportion to their efficiency as vectors, 
build up a carrier group in a community 
which is fluctuating and indeterminate in 
