Measurement of the absorption of silica particles using everted gut sac method. Measurement of the absorption of silica particles in rat intestine by means of the everted gut sac method combined with an inductively coupled plasma optical emission spectrometer. Intestinal sacs were incubated in solutions of the indicated silica particles (12.5 mg/mL) for 45 min. Values are expressed as mean ± SD (n = 5 to 12). *P < 0.01 and **P < 0.05 compared with the control group.