Proliferation-promoting intercellular hormones

Abstract

A comparison was made of the effects of rapid killing and of slow injury. The yield of proliferation-promoting intercellular hormones was, within limits, closely proportional to the time required to kill the cells. The yield of active factors was compared with the number of cells killed and found to increase rapidly before appreciable killing took place. The yields from cells injured in various media were compared and found highest when the medium contained carbohydrate, nitrogenous substances, phosphoric acid etc. CO2 was found to increase the yield of active factors in the intercellular fluids without killing the cells. Cells exposed to lethal ultraviolet before grinding yielded more potent prepns. than cells irradiated after grinding. Cells irradiated with lethal u.-v. after they were killed by boiling yielded less potent preps. than those irradiated before boiling.