lipids cannot be excluded, the present study demonstrating the phagocytic activity of this cell suggests that the radioactive material was ingested by the cell as a phospholipid lying free in the alveoli. Thus it is proposed that the nonciliated bronchiolar cell is the major site of pulmonary phospholipid production (presumably surfactant), while the large alveolar cell is a phagocytic cell responsible for the clearance of lipids as well as other materials from the alveolar area. ALBERT H. NIDEN Department of Medicine, University of Chicago, Chicago, Illinois 60637 SG, secretory granule. phagocytic activity. Ciliated cells are present in the terminal bronchiole but disappear in the respiratory bronchiole, well before the alveoli are reached. Thus the major portion of this bronchiolar secretion is not exposed to ciliary activity. These secretion granules did not stain with periodic acid-Schiff, Alcian blue, or Sudan black, indicating the absence of mucopolysaccharides, acid mucopolysaccharides, and free lipids. However, the granules did stain with Sudan black—acetone, Baker’s acid hematin, and silver hydroxylamine in an aqueous ‘solution (Fig. 4A), indicat- (10) were observed within 5 minutes at the apex of the Clara cells (Fig. 4B). The presence of positive granules after tissue extraction of free lipids demonstrates the ability of these cells to synthesize phospholipids from fatty acids. Although pulmonary surfactant has not been completely identified, it has been characterized as a phospholipid (71). Thus, until pulmonary surfactant has been more precisely identified, it is only a presumption that the phos- pholipid produced by the Clara cell is surfactant. The large alveolar cell was the only other cell which incorporated tritiated palmitate and acetate. Although the possibility that this alveolar cell is also capable of synthesizing phospho- . 2. R. E. Pattle, Physiol, Rev. 48, 48 (1965); M. E. Avery and S. I. Said, Medicine 44, 503 (1965). 3. J. A. Clements, Physiologist 5, 11 (1962). 4, C. C. Macklin, Lancet 1954-I, 1099 (1954); M. Klaus, O. K. Reiss, W. H. Tooley, C. Piel, J. A. Clements, Science 137, 750 (1962); S. Buckingham, W. F. McNary, J. E. Sommers, ibid. 145, 1192 (1964); K. Bensch, K. Schaefer, M E. Avery, ibid. p. 1318; K. E. Schaefer, M. E. Avery, K. Bensch, J. Clin. Invest. 43, 2080 (1964); M. M. Orzalesi, E. K. Motoyama, H. N. Jacobson, Y. Kikkawa, E. O. R. Reynolds, C. D. Cook, Pediatrics 35, 373 (1965); S. I. Said, R. M. Klein, L. W. Norrell, Y. T. Maddox, Science 152, 657 (1966). . M. Clara, Z. Mikrosk, Anat. Forsch, 41, 321 (1937). C. C. Macklin, Lancet 1954-I, 1099 (1954); M.Klaus, O. K. Reiss, W. H. Tooley, C. Piel, J. A. Clements, Science 137, 750 (1962); J. U. Balis and P. E. Conen, Lab. Invest. 13, 1215 (1964); K. Bensch, K. Schaefer, M. E. Avery, Science 145, 1318 (1964); Y. Kikkawa, E. K. Motoyama, C. D. Cook, Am. J. Pathol. 47, 877 (1965). . D. D. Sabatini. K. Bensch, R. J. Barrnett, on ing the presence of a phospholipid (9). Following the injection of tritiated palmitate or acetate intraperitoneally, autoradiographically positive granules References and Notes . G. Popjack and M. Beekmans, Biochem. J. 47, 233 (1950); J. M. Felts, Physiologist 5, 139 (1962); R. J. Havel, J. M. Felts, C. M. van Duyne, J. Lipid Res. 3, 297 (1962); J. M. Felts, Health Physics 10, 973 (1964); W. R. Harlan, Jr., S. I. Said, C. L. Spiers, C. M. Banerjee, M. E. Avery, Clin. Res. 12, 291 (1964); H. O. Heinemann, Bull, N.Y. Acad. Med, 40, 74 (1964); E. G. Tombropoulos, Science 146, 1180 (1964); K. Nasr and H. O. Heinemann, Am. J. Physiol. 208, 118 (1965); J. M. Felts, Med. Thorac. 22, 89 (1965); S. Buckingham, H. O. Heinemann, 8. C. Sommers, W. F. McNary, Am. J. Pathol. 48, 1027 (1966); A. Naimark, J. Appl. Physiol. 21, 1292 (1966). ~ normal mouse. (A) Bronchiolar cells at left with development of secretion granules (arrows). Brondroplets collecting at apex of cell (SG). C, ciliated secretory granule from apex of bronchiolar cell. nw Fig. 3. Terminal bronchiole from well-formed Golgi area and early chiolar cell at right with secretory cells; Ci, cilia. (B) Extrusion of J. Cell Biol, 17, 19 (1963), . A. B. Novikoff, in Lysosomes, A. V. S. de Reuck and M. P. Cameron, Eds, (Little, Brown, Boston, 1963), p. 36. 9, M. C. Berenbaum, Quart. J. Microscop. Sci. 99, 231 (1958); C. W. M. Adams, O. B. Bayliss, M. Z. M. Ibrahim, J. Histochem. Cy- tochem. 11, 560 (1963). 10, L. G. Caro and R. P. van Tubergen, J. Cell. Biol. 18, 173 (1962). 11. M. H. Klaus, J. A. Clements, R. J. Havel, Proc. Nati. Acad. Sci. U.S. 47, 1858 (1961); R. E. Pattle and L. C. Thomas, Nature 189, 844 (1961); M. E. Abrams and F. B. Taylor, Jr., Physiologist 7, 78 (1964); E. S. Brown, Am. J. Physiol. 207, 402 (1964); T. Fujiwara, H. Hirono, T. Arakawa, Tohoko J. Exptl. Med. 85, 33 (1965). Fig. 4. (A) Nonciliated bronchiolar cells stained with silver-hydroxamate reaction, embedded in Epon and counterstained lightly with Toluidine Blue. Granules at apex of bronchiolar cell stain positive for phospholipid. (B) Autoradiography of terminal bronchus 5 minutes after injection of tritiated palmitate intraperitoneally. Positive granules are at apex of bronchiolar cell. 1324 12. Supported by grants from the National Heart Institute (H-6918) and NSF (GF-189). I am indebted to Professor E. Yamada, Kyushu University, Fukuoka, Japan, under whose guidance and encouragement this study was initiated. I am grateful to Phyllis Fogel for her technical assistance. 15 June 1967 SCIENCE, VOL. 158