372 
EXPERIMENTS ON MIASMA. 
Struck with this phenomenon, I gathered at Higuerote a 
considerable quantity of branches and roots, for the purpose 
of making some experiments on the infusion of the man- 
grove, on my arrival at Caracas. The infusion in warm 
water had a brown colour and an astringent taste. It con- 
tained a mixture of extractive matter and tannin. The 
rhizophora, the misletoe, the cornel-tree, in short, all the 
plants which belong to the natural families of the loran- 
theous and the caprifoliaceous plants, have the same proper- 
ties. The infusion of mangrove-wood, kept in contact with 
atmospheric ah’ under a glass jar for twelve days, was not 
sensibly deteriorated in purity. A little blackish ilocculent 
sediment was formed, but it was attended by no sensible 
absorption of oxygen. The wood and roots of the mangrove 
placed under water were exposed to the rays of the sun. I 
tried to imitate the daily operations of nature on the coasts 
at the rise of the tide. Bubbles of air were disengaged, and 
at the expiration of ten days they formed a volume of thirty- 
three cubic inches. They were a mixture of azotic gas and 
carbonic acid. Nitrous gas scarcely indicated the presence 
of oxygen.* Lastly, I set the wood and the roots of the 
mangrove thoroughly wetted, to act on a given volume of 
atmospheric air in a phial with a ground-glass stopple. The 
whole of the oxygen disappeared ; and, far from being super- 
seded by carbonic acid, lime-water indicated only 0 02. There 
was even a dimunition of the volume of air, more than cor- 
respondent with the oxygen absorbed. These slight experi- 
ments led me to conclude that it is the moistened bark and 
wood which act upon the atmosphere in the forests of man- 
grove-trees, and not the water strongly tinged with yellow, 
forming a distinct band along the coasts. In pursuing the 
different stages of the decomposition of the ligneous matter, 
I observed no appearance of a disengagement of sulphuretted 
hydrogen, to which many travellers attribute the smell per- 
ceived amidst mangroves. The decomposition of the earthy 
and alkaline sulphates, and their transition to the state of 
sulphurets, may no doubt favour this disengagement in many 
littoral and marine plants ; for instance, in the fuci : but I 
am rather inclined to think that the rhizophora, the avicen- 
* In a hundred parts there were eighty-four of nitrogen, fifteen of car- 
bonic acid gas that the water had not absorbed, and one of oxvgen. 
