Abstract
Digestion of adult tissue with trypsin has been shown to stimulate its initial growth in vitro. This stimulation appeared to result from the removal of an inhibitory material from the tissue due to the proteolytic action of the trypsin. This paper shows that the fluid after the digestion contains material which inhibits the initial growth of adult chicken aorta tissue. This tissue inhibitor has been obtained from chicken, dog, and sheep aortas. It is partly precipitated by an equal volume of alcohol, and is more completely precipitated by the further addition of CaCl(2) (plus a little NaOH). The inhibitor is destroyed at 100 degrees C. but usually withstands 58 degrees C. for 20 minutes. Moderate tryptic digestion renders it soluble without destroying it. It sometimes withstands dialysis, but at other times is lost. Its physical and chemical properties, as far as we know them, coincide with those of lactenin (a bacteriostatic substance in milk). Lactenin was found to inhibit adult tissue growth; but the tissue inhibitor failed to restrain bacterial growth. This tissue inhibitor is believed to play a rôle in limiting the growth of tissue in the adult animal.