118 CONTRASTS OF CLIMATE. 



So, were there unaccountable moulds and mildews, in the 

 driest periods of the pestilential years, in New York, Phi- 

 ladelphia, and Natchez. Sometimes but one kind of germ 

 is stimulated, as in the case of the apples already cited, 

 sometimes many are excited, as in some years of great and 

 general "pomonal" luxuriancy. So is it with the fungi, 

 as manifested by the extension of only one disease, or 

 the co-existence of many. Of all plants, the cryptogami 

 are the most capricious, or most susceptible of modification 

 by unseen causes. Hence the quality of the season is 

 scarcely ever an index to the morbid condition of any 

 particular year, although heat, moisture and a redundant 

 vegetation are general precursors of malarious action. 



We can, on our hypothesis, easily explain the arrival 

 of the annual morbid orgasm, after the rains of one coun- 

 try, and in the rains of another. Whether hot or cool, 

 wet or dry, the sickly season is the harvest time of the 

 fungi, which lie tied by time and not by circumstance, 

 until their customary period of activity has arrived; when 

 more or less stimulated by moisture, and food, and elec- 

 tricity, they show a feeble or a strong fecundity. 



On our supposition alone, can we account for the sudden 

 effect, in Africa, of the first rains. The dry season bakes 

 the earth to a crust. The lesser vegetation is dried up 

 under the scorching glare of a tropical sun, and nature 

 seems almost at a stand. That is there, the season of 

 health. But the rains commence, and almost in a moment, 

 arises a morbid influence inexplicable by reference either 

 to heat or moisture, or any ordinary decomposition. " The 

 rain had scarcely commenced," says Mungo Park, "before 

 many of the soldiers were affected with vomiting. Others 

 fell asleep, and seemed as if intoxicated. I felt a strong 

 inclination to sleep during the storm, and as soon as it 



