In the gas experiments Davy ran considerable risks. His respiration of nitric oxide which may have combined with air in the mouth to form nitric acid (HNO3), severely injured the mucous membrane, and in Davy's attempt to inhale four quarts of "pure hydrocarbonate" gas in an experiment with carbon monoxide he "seemed sinking into annihilation." On being removed into the open air, Davy faintly articulated, "I do not think I shall die," but some hours elapsed before the painful symptoms ceased. Davy was able to take his own pulse as he staggered out of the laboratory and into the garden, and he described it in his notes as "threadlike and beating with excessive quickness".