162 REPORT OF THE HARVARD AFRICAN EXPEDITION 
investigators found that of the two hundred and twenty-five men who were 
engaged for four and a half months in mapping and who were taking one gram 
of quinine daily, only fourteen, or six per cent showed clinical symptoms of mala- 
ria. Only after the quinine was discontinued did the actual amount of infection 
in the command become manifest through the appearance of symptoms of mala- 
ria in one hundred and six persons, or forty-seven per cent. This work, although 
in conformity with Yorke and Macfie’s conclusions that quinine does not prevent 
malarial infection, does not confirm their observation to the effect that con- 
tinued use of the drug for from ten days to two weeks after exposure to the 
insect bite always prevents any subsequent malarial paroxysm. McNabb and 
Stewart conclude that under field conditions in a hot climate where men are 
undergoing physical hardship one gram of quinine will prevent the development 
of symptoms of malaria in men exposed to infection and will keep them on 
duty, and that although ‘‘quinine prophylaxis” will not prevent infection, it 
has great military value since it will enable troops to accomplish a mission in a 
malarious region. These observations also demonstrate that although quinine 
in the dosage given did not prevent malarial infection in forty-seven per cent of 
the persons concerned, the fact that over fifty per cent of them lived and worked 
for four and a half months in a most malarious region without developing symp- 
toms of malaria even after discontinuing the quinine, indicates that even though 
infection may not have been prevented, a considerable number of persons must 
have been rid of the infection almost immediately after its occurrence. Craig 
believes that it is impossible that over fifty per cent of a command could escape 
the development of clinical malaria under such conditions had quinine not been 
administered. He also suggests that the effect of a larger prophylactic dose of 
quinine than one gram should be investigated, since he thinks it possible that 
a dose of 1.5 grams might be successful in freeing the vast majority of persons 
from infections that might occur before the appearance of symptoms. 
