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cause the three clinical types of malarial fevers, Quotidian, Tertian
and Quartan, which are so commonly met with. It will be appa-
rent that if a parasite should, for some reason or other, complete its
asexual cycle in a less period than 24, 48, or 72 hours, a different
clinical type of fever will result, and also that a different clinical
type may be produced by the presence in the blood of two or more
groups of parasites which sporulate at different times.
The three species of malaria parasites referred to above are
called respectively:-
(1)  The Malignant Tertian parasite.
(2)  The Benign Tertian parasite.
(3) The Quartan parasite.
The general description of the life cycle of the malaria parasite
in man and in the mosquito which I have already given, applies
equally to all these species, but they differ from each other not only
in the time which they take to complete their asexual cycles respec-
tively, but also in other particulars, such as their size and appear-
ance, their amœboid movements, the character of the pigment they
produce, the number of segments into which they divide up, and
the characters of the sexual forms. These differences are considered
sufficient for them to be regarded as distinct species.
I shall describe first the results of an infection with Benign
Tertian parasites, because this is the species most commonly met
with in India, and afterwards note the differences which result
from infections with the other two forms.
1. Benign Tertian infection.-Supposing a man to have been
bitten by a mosquito infected with the sporozoites of the Benign
Tertian parasite, he will probably not feel any ill effects until about
twelve or fourteen days afterwards. This is the incubation period
during which the parasites have been gradually multiplying in his
blood, but have not been present in sufficient numbers to cause any
symptoms. Towards the end of the period he may feel some aching
of the bones, headache, or other premonitory symptoms, and his
temperature may be somewhat raised. After these indefinite symp-
toms have gone on for a day or two the regular attacks of " ague "
begin. These consist of a series of attacks of fever which recur, in
infections with the Simple or Benign Tertian parasite, at definite in-
tervals of 48 hours. Each attack is represented clinically by a
"cold" stage, a "hot" stage, and a "sweating" stage. At the