172 
MALARIA 
TABLE IX 
Parasite Density at the Time of Clinical Onset of Primary Induced Vivax Malaria 
Parasite 
Inoculation 
by 
Parasites per 
cmm on day 1st 
elevation of 
temp. 
Onset 
preceding 
detection 
of para¬ 
sites 
in days 
Onset 
and para¬ 
sites on 
same day 
Parasites first observed 
on different days pre¬ 
ceding onset 
Total 
3 2 
1 
1 
2 
3 
4 
5 
6 
7 
P. vivax 
Mosquitoes 
Fewer than 10 
... 1 
5 
10 
6 
1 
... 
23 
11-50 
. 
2 
6 
7 
3 
1 
... 
19 
51-100 
. 
3 
2 
3 
... 
8 
101-500 
... 
1 
2 
1 
1 
5 
501-1000 
... 
... 
1 
1 
More than 1000 
Total 
0 1 
5 
12 
16 
11 
8 
1 
1 
1 
... 
56 
Blood 
Fewer than 10 
... 1 
3 
2 
2 
8 
11-50 
... 
1 
... 
1 
51-100 
... ._ 
1 
... 
1 
101-500 
3 
... 
1 
1 
1 
... 
6 
501-1000 
. 
... 
... 
... 
... 
... 
More than 1000 
... 
1 
1 
1 
1 
4 
Total 
0 1 
0 
3 
3 
2 
4 
3 
1 
2 
1 
20 
is not a constant pyrogenic threshold for 
all strains of this parasite. 
A still higher threshold is observed at the 
onset of relapses in chronic infections. 
Thus studies by Sinton et al. (1931) indi¬ 
cate that under this circumstance a pyrexial 
level of about 5,000 per cmm prevails. 
Our own experience leads to the view that 
varying susceptibility of patients rather 
than varying virulence of different strains 
of parasites is chiefly responsible for the 
variations in density noted at the onset. 
The Parasites in Relation to the 
Symptoms 
The intermittent and periodic febrile 
paroxysms experienced by patients with 
an active malaria infection are, as first 
shown by Golgi, directly ascribable to the 
maturation and asexual division of a brood 
or generation of parasites. The relation¬ 
ship is shown in the accompanying figure 
(Pig. 4). Smears made at the onset and 
during a few days shortly thereafter show 
a great diversity in the development of the 
parasites observed at any hour, although 
even at this period a majority may be in 
the same stage. In this circumstance the 
patient may exhibit a remittent, rather 
than an intermittent, fever. As the infec¬ 
tion progresses the parasites, for reasons 
not clearly understood, tend to become 
more closely synchronized, so that all of a 
given generation complete their develop¬ 
ment within a few hours of each other. 
The generations in falciparum infections 
do not usually become as closely synchron¬ 
ized as in the case of the other species. 
Several may mature at different periods on 
the same day, thus greatly prolonging the 
duration of the fever, which may show 
several distinct peaks. 
A schizogonous generation of P. vivax 
and P. falciparum requires 48 hours and 
one of P. malariae requires 72 hours for its 
completion. During the growth of the 
parasites the infected person will not pre¬ 
sent any markedly significant symptoms 
connected with the cycle. With the com¬ 
pletion of schizogony and the liberation of 
the merozoites from the divided schizonts 
in the shells of the erythrocytes in which 
they were formed, the patient, provided the 
pyrogenic density of parasites is attained, 
