An electron microscopic study of normal mouse lung and the early diffuse changes following uracil mustard administration

The fine structure of normal mouse lung and the early changes induced in respiratory tissue by uracil mustard, administered in a manner and dosage similar to that used by Abell et al. (1) are described. Two types of pulmonary surface epithelial cell (types I and II) were identified. No cell considered to be transitional between these two types was noted. A third type of surface epithelial cell described in rats was not seen. Two apparently distinct forms of alveolar (septal) cell were recognized. These two forms probably correspond to the two types previously identified by light microscopy. An increase in the number of ribosomes and the amount of rough endoplasmic reticulum was observed in all the types of cell in respiratory tissue during the first 6 weeks of treatment, in addition to the intranuclear inclusions seen in type II cells 4 hours after the initial injection of uracil mustard. No changes were noted in the bronchiolar epithelium.