L. Karlstein 1954 Oiling Expt. Bufo boreas (44) July 5 Laboratory oiling experiment. I placed 4 tadpoles and one metamorphosed toyla in a refrigerator dish 4 1/2" x 4 1/2" x 3" filled with 600 cc. of fresh water. I gently poured 20 cc. of diesel oil over the surface. It coalesed into large droplets at first but immediately dispersed outward. The first 10 cc. covered only 2/3 of the water surface, not extending toward the outer edges. But with 20 cc. of oil the entire surface became covered with a film. The two Bufo tods have hind legs 2-3 mm. long. Their total length averages 26 mm.; body length 12 mm. Toyla tods at different developmental stages. One lacks my limbs, body length 12/3 mm.; second has 10 mm. long hind limbs, body length 13.5 24 mm. Both have total length about 28 mm. The metamorphosed toyle has almost completely resorbed its tail which juts out 2 mm. Body length 11 mm. It crawls up sides of dish readily in spite of oil film over its body. Oiling at 9:30 A.M. Tods active immediately and swim to surface in attempt to secure oxygen in the surface film. These animals are probably further along in develop- ment than those exposed to oil in natural pond near Yosemite Valley. Animals probably not severe by 10 A.M. The tods by swimming straight up from bottom (water 1 1/2" deep) seem to break through film, at least an air