The various notices I have had the honour of presenting under this title have had the effect of demonstrating that changes of barometric pressure, if we except very rapid and great decompressions, have no physico-mechanical action upon animals and vegetables, but influence them exclusively from a chemical point of view. Below the normal pressure of the air too feeble tension of oxygen tends to promote asphyxia : above, too strong a tension tends to increase those formidable accidents which I have designated, somewhat paradoxically I admit, by the expression, poisoning by oxygen ; and hence the conclusion at which I have arrived, that all danger may be avoided by varying the oxygenous richness of the air inversely to the variation of pressure.