The experiments have shown that extracts of tissues and tissue juices, under certain conditions, accelerate the growth in intro of the connective tissue from about three to forty times. This activating power was found in many tissues. It was much more marked, however, with the extracts of embryos, of adult spleen, and of the Rous sarcoma. The power diminished directly with the dilution of the extracts, and appeared not to apply to the tissues of a heterologous animal. The power was reduced when heated at 56° C., and removed when heated at 70° C. It was diminished markedly by filtration through a Berkefield filter and was completely suppressed by filtration through a Chamberland filter.

Possibly the finding of the activating power of tissue extracts will have no immediate practical application. Nevertheless, it may be indirectly useful by leading to the discovery of some of the factors determining the growth of tissues and of the unknown laws of cell dynamics, and may ultimately throw light on the mechanism of the cicatrization of wounds.

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