Abstract
1. A strain of connective tissue is still very active after more than 7 years of life in vitro. 2. The rate of growth of the fragments of tissue can be measured accurately and used for testing the action of many different factors on the growth of connective tissue cells. 3. The rate of growth of the strain is at least as rapid as it was 5 years ago, and may be more active. 4. The connective tissue cells appear to have the power of multiplying indefinitely in a culture medium, as do microorganisms.