In 1799, a very young chemist ”” about 21 years old ”” inhaled a lot of carbon monoxide directly into his lungs, keeled over, was seized by agonizing chest pains, staggered into his garden, got giddy, became nauseous, went to bed, recovered ”” and then, a few days later, he did it again.
Welcome to the world of 18th century science. Richard Holmes, in his book Age of Wonder, describes how young Humphry Davy went looking for a possible cure for tuberculosis. He tried inhaling very different gases, hoping to improve respiration. In a very un-20th century way, he matter-of-factly experimented on himself, his pets, his friends and even friends of friends.
Listen to it all (about 7 3/4 minutes). A terrific piece on the history of science.