30 On Tropical Miasmata. 
* All these circumstances lead to the suspicion that it is 
not sulphuretted hydrogen on which depend the diseases pe- 
culiar to the coast of Africa, but organic matter of animal 
composition. In considering that this matter is formed dur- 
ing the spontaneous decomposition of vegetable substances by 
an incomplete oxidation of their hydrogen and carbon, it is 
very probable that, when vegetable substances are oxidized 
by the oxygen of sulphates, a matter of a similar kind is also 
formed. As that matter formed by oxidation at the expense 
of atmospheric air is volatilized, it is to be supposed that the 
same is done when such a matter is formed by another action. 
These views being correct, such matters would be evolved 
together with sulphuretted hydrogen. 
“As it is intended by the medical officers of the Expedi- 
tion, on approaching the coast of Africa, to test the water at 
different distances, I venture to add the desirableness of test- 
ing also the atmospheric air by means of concentrated sul- 
phuric acid, placed in a vessel on the windward side of the 
deck, and protected against insects. It is scarcely to be 
doubted that the more the air becomes infective, the more the 
sulphuric acid will be blackened. 
« As for the destructiveness of sulphuretted hydrogen, sup- 
posed in The Friend of Africa, | may be permitted to suggest 
a few remarks. It is true that this gas is very deleterious, 
only ,;55 part of it in the atmosphere kills a bird; but in 
what manner does this gas act on animal life? When not 
present in such a proportion as to kill a man instantly, it 
causes inflammation in the lungs. Workmen cementing steam- 
vessels in the inside, where the cement, after some time, dis- 
engages sulphuretted hydrogen, offer instances of this kind. 
When this occurs before the workman has left the vessel, he 
risks, at least, a dangerous inflammation on the chest. It is 
to be supposed that sulphuretted hydrogen, when diluted with 
air in such a proportion as still to be injurious to animal life, 
will not affect in a different manner to it. But are the dis- 
eases, peculiar to the coast of Africa, of such a kind as those 
produced by sulphuretted hydrogen ? 
“There are many places where this gas is evolved in large 
quantities ; for instance, in the Solfatara of Pozzuoli, in the 
