On Malaria. 311 
veins; but what it is, which intercepts its passage across a’ garden 
or an open street ; whether it is limited by some meteorological phe- 
nomenon ; or whatever the cause is, it has hitherto eluded dis- 
covery. Its movements cannot generally be anticipated with cer- 
tainty, for it is only ina few cases that it is so strangely exact. 
Several circumstances must concur in common instances in con- 
veying it to greater or less distances. These are, its greater or less 
concentration, the favor of the wind which should not be too strong, 
and the precise amount of fog or moisture. If there is too much wa= 
ter, it will be diluted ; if the wind is too strong, it will be dispersed; if 
the sun is too hot, it will be dried up, and will’separate from moisture, 
which alone unfolds its existence. ‘This occult property is doubtless in- 
noxious, as it certainly isunknown. — It is to such unseen counteracting 
forces that those differences are owing in successive seasons, for which 
we can assign no cause; such as a healthy year succeeding to one 
of great mortality, a healthy place becoming sickly, and the reverse : 
That the laws which control the phenomena of malaria are uniform, 
eannot be doubted, although our powers of observation are not al- 
ways sufficient to discover the causes, or to reconcile apparant disa- 
greements; butif we can arrive at data which will enable us to rem- 
edy, or will teach us to shun the evil, we need not repine if the ambi-+ 
tion of science is checked in its endeavors to fathom all its mysteries. 
~The occurrence of intermittents in hill countries has led some to 
imagine that the causes were as various as the localities; or perhaps not 
chargeable to external agencies, but inherent in certain conditions of 
the human constitution. ‘The debility or predisposition of individ- 
uals, is undoubtedly the reason why some are seized while others es- 
cape, but this does not impugn the argument, that this form of disease, 
viz. intermitting fever, is owing to'an external and material agency, 
gh modified by an endless variety of cireumstances. One 
among many ways of accounting for this seeming anomaly, is that al- 
ready remarked, that it is conveyed in currents by the winds. Vol- 
ney States that “high grounds in Bengal, with the most promising 
of upland scenery, are infested with wasting intermit- 
tents, called hill fever, from the poisonous effluvia wafted by the 
Monsoons from the distant marshy plain.” The same writer adds 
“that there are high lands in Corsica and Italy wholly uninhabitable, 
because, though far remote from damp and boggy places, the malady 
of low lands and bogs is brought thither by the winds whieh blow over 
