In the course of another series of experiments, it was noted that epithelial lined cavities were occasionally formed as a by-product. Realizing the possible clinical importance of this finding, we undertook a group of experiments with the hope that a practical method of producing epithelial lined tubes and sacs might be developed. METHOD The study was made on a series of twelve dogs on each of which two epithelial lined cavities were produced. Under ether anesthesia, the abdomen was shaved and washed with green soap followed by benzine and alcohol. The skin was then painted either with 5 per cent picric acid in alcohol or with 2 per cent mercurochrome-220 soluble in alcoholacetone solution.1The latter was found to be much more efficacious than iodine in cleansing the skin and somewhat better than the picric acid solution. A whole thickness graft was then cut, its shape depending on whether