PLASMODIUM MALARI&. 633 
their presence alone the diagnosis must often rest: (1) 
In severe acute cases after the administration of much 
quinine; (2) in remittent malarial fevers; and (3) in 
chronic malarial fever and cachexia. They persist in 
the blood long after all traces of parasites have dis- 
appeared. The identification of free malarial pigment 
is usually hazardous, and the diagnosis of malaria 
should never be based on its presence alone (Ewing). 
Inoculation Experiments. Malarial infection can be 
transmitted directly from man to man by subcutaneous 
or intravenous inoculation of malarial blood. This was 
shown first by Gerhardt in 1884, Later experiments, 
chiefly by Italians observers, have confirmed Gerhardt’ s 
investigations, and almost in every instance the variety 
of organism introduced has been reproduced. It has 
also been experimentally shown that the ague paroxysm 
is associated with the segmentation of enormous groups 
of intracorpuscular amcebe, the symptoms being prob- 
ably due, as Bacelli suggests, to toxins liberated during 
sporulation or to substances set free in the blood by 
the rapid destruction of a large number of its corpuscles. 
The period of incubation is from eleven to twelve days 
in the regular intermittents and from two to five days 
in the irregular autumnal fever. 
Active phagocytosis goes on in all forms of malarial 
infection, but its true significance is still undetermined. 
That many parasites are devoured by the leucocytes, 
especially in the spleen, is certain. This apparently 
takes place during or after sporulation. But sponta- 
neous recovery may also be due to the death of the 
plasmodia. It is not improbable, however, that the 
phagocytes contribute to the process of recovery, even 
if they are not the chief factors in it. 
