ABSTRACT
Knowledge of the mind-altering capabilities of certain chemicals goes as far back as recorded history. Indeed, natural, and more recently, synthetic chemicals have been used by humans to induce mind states of euphoria, hallucinations, and apparent well-being. Many environmental and occupational neurotoxic substances have properties similar to those of, alcohol and recreational drugs, initially producing excitatory effects; as the dose increases in quantity or in time, these same neurotoxic substances depress the nervous system. Children are familiar with Lewis Carroll's febrile "mad-hatter" in Alice in Wonderland, who was exposed to mercury vapors in the manufacture of felt hats. Ramazinni in "De morbis artificum diatriba", published in 1700, notes that the artists of Modena, Italy, where he lived and worked, manifested similar behavior and nervous system deficits that he attributed to their exposure to a wide variety of chemical agents86 •
Different types of studies have provided an overall portrait of nervous system changes along this continuum. In experimental set-ups, healthy human
volunteers are placed in air-tight chambers, where they are exposed to specific levels of toxicants; these controlled human chamber studies have served to document acute neuropsychological and psychophysical alterations in healthy subjects. Surveys of occupationally and environmentally exposed active populations have provided information on early behavioral changes associated with long term, low exposures, while clinical reports and epidemiological studies have described the more lasting, severe changes associated with intoxication.
