Foreign material observed by light microscopy (A) and polarized light (B). A. The figure is a low magnification image of MWCNT deposition in the lungs. Macrophages in alveolar spaces of the right apical lobe of the lung contain intracytoplasmic, black, elongate to finely granular particulate material (presumptive MWCNT). (40x). B. Using polarized light, the low magnification image demonstrates presumptive MWCNT are seen in macrophages in the right apical lung lobe of mouse treated with MWCNT. The material in the macrophages are birefringent. (40x).