Fig. 2. Light microscopy. Light microscopy examination of lung tissue after Leder staining revealed a significantly higher number of pulmonary leukocytes in healthy animals after 120 (group 120 , D ) and 240 min (group 240 , E ) of mechanical ventilation compared with the unventilated control animals (group C , A ). Significantly lower numbers of pulmonary leukocytes were found in the animals that were allowed to recover (group R , F ) compared with animals ventilated for 240 min (group 240 , E ). No differences were found between unventilated controls (group C , A ) and the animals that were allowed to recover (group R , F ). For the results of leukocyte counts, see table 2. ( A ) Unventilated control animals. ( B –E ) Healthy animals receiving mechanical ventilation for 30, 60, 120, and 240 min. ( F ) Animals that were allowed to recover for 2 days after being ventilated for 240 min (group R). Magnification: 750×.