The French scientist Alfred Maury (1817–1892) published his Sleep and Dreams in 1861. Prior to this, he kept a dream diary, paying extra attention to the circumstances he believed contributed to their content and intensity. Among the external factors on which he placed great importance, diet and environmental changes were particularly important to him. He also paid extra attention to the hypnagogic hallucinations that appeared in the moments before he drifted off to sleep. It was his belief that these provided an “embryogenesis” of his subsequent dream images.
In experiments he conducted later in his career, he served as the primary subject while an assistant introduced various stimuli to his senses after he entered into the rapid eye movement state of sleep. These stimuli were both auditory and olfactory. The hope was that he would be able to report the effects of outside stimuli on the content of his dreams. On one occasion, his assistant tickled his lips and the inside of his nostrils with a feather and Maury dreamed that the skin in those places was being ripped from his face by a mass of burning pitch. In a different instance, heated iron was held close to him and Maury reported a dream in which robbers were putting his feet in fire in an effort to get him to reveal the location of money.
The experiments also indicated that scents could factor into dream content. When his assistant held a burning match close to his nose Maury dreamed that the magazine of his ship blew up; he also dreamed of a perfume shop when exposed to the scent of a bottle of cologne. The results of these tests lend validity to the theory that the environment affects what we experience while in a sleeping state.