Electron microscopic studies of various cells in the alveolar wall of mice with special reference to spheroid alveolar epithelial cells after intravenous injection of squid-ink (sepia-melanin) solution.

The effect of an intravenous injection of squid-ink (sepia-melanin) solution on adult mouse spheroid alveolar epithelial cells was observed by the electron microscope. Sepia-melanin particles were seen in all alveolar wall cells examined that seems to suggest the entrance of sepia-melanin particles into the spheroid alveolar epithlial cells from the alveolar blood capillary. In cases of large penetrations of sepia-melanin particles into spheroid alveolar epithelial cells, a greater increase was found in the intramitochondrial granules. In addition, the so-called inclusion body believed to be formed by the degeneration of mitochondria had very high electron density and its quantity was abundant. On the contrary, in cases where the quantity of sepia-melanin entrance into the spheroid alveolar epithelial cell was small, neither an increase of intramitochondrial granules, an increase of the electron density nor an increase in the quantity of specific inclusion body was found.