Of these carbon dioxide and water are the most prominent.
Humans require relatively little oxygen, and plants are constantly transforming the carbon dioxide we exhale back into useful oxygen.
When sulphur is burned in air or oxygen, sulphur dioxide is produced, which is a powerful disinfectant, used to fumigate rooms which have been occupied by persons suffering from some infectious disease.
Sulphur dioxide and sulphuretted hydrogen are present in volcanic exhalations and in many mineral waters.
Fungal and phanerogamic parasites can make no use of stich substances as carbon dioxide, but draw elaborated products from the bodies of their hosts.
