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10 months in mild to moderate cases. 'out may take up to 3 years in serious cases. The threshold level at which neuropathy occurs has not been firmly established but symptoms have been observed in people exposed to concentrations ranging from 10 to 200 ppm for 9-12 months. �J In animals, signs of narcosis are seen after mice are exposed to vapor levels of 16,000 ppm for 5 minutes. Death generally occurred at concentrations between 43,800 and 52,000 ppm after 9-119 minutes. The oral LD., is cited as 24 mL/kg for 14-day-old rats and 49 mL/kg for young adult rats. Tong-term inhalation experiments in rats suggest that the first signs of neurotoxicity appear after they are exposed to levels of 200 ppm for 24 weeks. This higher threshold to induce neurotoxicity in -- animals may be due to differences in metabolism. Specifically, 2-hexanol is the chief metabolite in animals. while 2,5-hexanedione which is neurotoxic. predominates in man. Chronic topical application of a solvent containing 35.21 n-hexane caused axonal swelling and Myelin degeneration in chicks. No clinical signs were seen. Dosage was 1 g/kg/day for 64 days. In rabbits, topical application of 0.5 ML/day for up cc 10 days caused redness, irritation and scab formation. -- N-hexane is neither carcinogenic or teratogenic. One in vivo study in rats that inhaled 150 ppm for 5 days found an increased number of chromosome aberrations in the bone marrow cells. No studies an mutagenicity. reproductive toxicity or carcinogenicity in man were found (12,2930.1935) . j&gp_e_nrane Isopentane is a CNS depressant. Effects may include exhilaration, dizziness, headache, loss of appetite, nausea, confusion. inability cc do fine work. a persistent taste of gasoline and in extreme cases, loss of consciousness. Inhalation of up to 500 ppm appears to have no effect on humans. -Very high" vapor concentrations are irritating to the skin and eyes. Repeated or prolonged skin contact will dry and defac skim resulting in irritation and dermatitis. The LCs. in the mouse is estimated to be 1000 mg/L (12) . 2-Hethylvenrane (isohexane, 3-mechyipentane) No physiological data are available but isohexanes are expected to be mucous membrane irritants and to have a low oral toxicity. Ischexanes are predicted to have- narcotic properties and are documented to be cardiac sensitizers buc are not expected to have neurotoxic properties (12) . -- Cyclohexane Cyclohexane is a CNS depressant of low toxicity. Symptoms of r acute exposure are excitement, loss of equilibrium, stupor and coma. Rarely, death results due to respiratory failure. The anesthesia which is induced is weak and of brief duration bur- more potent than that 6/87 �.