98 
PROPHYLAXIS OP MALARIA. 
The number of malarial patients becoming “carriers” Avill vary, 
of course, in different localities, owing to conditions favoring the 
persistence of the infection, the type of infection present, the thor¬ 
oughness with which treatment is carried out, and perhaps other 
conditions with which we are yet unfamiliar. This subject has 
been most carefullv studied in the estivo-autumnal infections, and 
the data Ave possess sIioav beyond question that the percentage varies 
greatly and that the incidence of gametes in the peripheral blood 
can not be taken as a true index of their actual occurrence in the 
body, for in many instances it has been demonstrated that blood 
obtained by splenic puncture was rich in gametes Avhen none could 
be demonstrated in the peripheral blood. In my own experience 
gametes have been observed in a little over 33 per cent of all the 
cases of estivo-autumnal malaria Avhose blood I have examined, but 
I am convinced that a longer search in the majority of these patients 
would have considerably increased this percentage. In the instances 
of recurrent infections in Filipinos, Avhich I have had the oppor¬ 
tunity of studying, crescents occurred in fully 80 per cent and were 
as numerous in the adult Filipino as in the children. Most of these 
cases had received little or no treatment, and for this reason, I be¬ 
lieve, the percentage is practically what would be observed in un¬ 
treated individuals. From my own observations, I belieA^e that at 
least this percentage of cases of estivo-autumnal malaria will be¬ 
come “carriers” unless they are properly treated. 
We possess but little data regarding the percentage of patients in¬ 
fected with the tertian and quartan plasmodia in Avhom gametes de¬ 
velop, but, in my OAvn experience, I have found that these forms occur 
in about 50 per cent of the cases of infection admitted to hospital 
and in about 30 per cent of latent infections. 
For practical purposes, an individual who does not show gametes 
in the peripheral blood must be considered as incapable of transmit¬ 
ting infection to the mosquito, but this conclusion should not be ar¬ 
rived at from a cursory examination of the blood but onty after the 
most careful examination of at least two specimens, taken at different 
times, and, if possible, on different days, for these forms are often 
numerous in the peripheral blood at one time and practically absent 
at another. 
Estimation of the number of gametes in prophylaxis .—The ob- 
seiwations of Darling and Thomson have shown that a certain num¬ 
ber of gametes must be present in the peripheral blood in order to 
render the infected individual infective to the mosquito. In a very 
ingenious series of experiments Darling 53 arrived at the conclusion 
that the peripheral blood must contain at least 12 crescents per cubic 
centimeter, or more than 1 per 500 leucocytes , in order to be infective 
to the mosquito, and that patients whose blood contains this number 
