On Malaria, 41 



whole. There, the malaria and the fever commence at the 

 moment the rain falls; diminishing as the ground becomes 

 thoroughly wetted, and recommencing as it dries. The expla- 

 nation of all this ought to be obvious ; and the same analogy 

 governs all the hotter climates, as, though less conspicuously, 

 it does our own. Hence we explain, both as to our spring and 

 our autumn, the effects of heat following rain, or the reverse, 

 and the diseases which are consequent on those changes : and 

 thus it is, though more remarkably, in Italy, that a rainy 

 autumn increases the number and severity of fevers ; or, if the 

 summer has been unusually dry, that they often do not appear 

 till the commencement of the autumnal, or even the winter rains. 

 And hence, also, even with us, the occurrence of a single rainy 

 day or week, in the midst of the heats, will produce fevers ; 

 while the effect of this influence is such, that should there even 

 be an entire rainy summer, and the subsequent one be hot and 

 dry, this will be attended by an unusual production of malaria 

 and disease. 



And if I cannot detail all the various modes in which 

 these circumstances may be modified, and how their effects 

 may vary, it will be useful to make one remark on an error as 

 relating to it which is universal among us, and into which even 

 Lind has fallen. The error is, to think that the rain, the moisture, 

 or the cold is itself the cause of the diseases which follow this 

 state of things ; while it is obviously a case analogous to that 

 of Africa, if less severe, and the malaria is produced by these 

 circumstances on soils which I formerly pointed out, and which 

 Lind, like every one else, had neglected. But if I must pass 

 over many interesting and useful conclusions to be drawn from 

 these general principles, there is one fact which I must notice, 

 and it is this : — 



In spring, the combination of heat and moisture, easily ex- 

 plained, generates, most commonly, intermittents ; or the effect 

 of the malaria at this season differs from what it does in 

 autumn : while as the heat advances and the ground dries, this 

 kind of fever ceases to be produced, a new species, or the sum- 

 mer remittent, taking its place when the heat and the moisture 

 of autumn begin to act. But under peculiar seasons of heat 

 and moisture with us, it sometimes occurs, as it has doue 



