634 APPENDIX. 
With regard to immunity, we know that one attack 
of malaria may linger a long time, and seems rather to 
favor than to prevent a new infection. There is, 
however, a natural susceptibility to the disease which 
is very variable. Different races of men especially 
seem to possess in variable degree the power of resist- 
ance to malarial infection. This is shown not only in 
a diminished tendency to contract the disease, but also 
in the form by which they are affected. For instance, 
the negroes in the Southern parts of the United States 
are much less liable to contract malaria than the whites; 
and Martin reports that the Europeans living in Suma- 
tra are far more frequently and severely affected by 
malaria than the natives, who, if they are attacked at 
all, it is only with the simple intermittent tertian and 
quartan fevers. 
The Action of Quinine on the Parasites. Laveran 
showed that a solution of 1 to 10,000 of quinine, run 
under the cover-glass, would check at once the move- 
ments of malarial organisms. As demonstrated by 
Marchiafava and Celli, however, a like effect is pro- 
duced either by the water or by the salt solution in 
which the quinine is dissolved, and we meet with an 
almost insuperable difficulty in the study of the direct 
action of the drug upon the parasites themselves. 
Many careful experiments have been made to deter- 
mine the effect of quinine on the parasites circulating 
in the blood, and Romanowsky, Golgi and others have 
reported a diminution in the activity of the amceboid 
movements. Osler stated that, as a result of careful 
hourly examinations made in a series of cases with a 
view of ascertaining the direct influence of full doses of 
quinine, he was unable to make up his mind that any 
