Objective To observe the seasonal change of Clock gene expression in blood lymphocytes in rats model with defensive-qi deficiency. Methods Twenty Sprague Dawley rats were randomly and equally assigned into control and model groups one week before spring equinox,summer solstice,autumnal equinox and winter solstice.Rats in control group were fed routinely,while those in model group were dealt with methods combining fatigue with alternate cold and heat stimulation to establish defensive-qi deficiency model. Cl...