Abstract
Summary
The serum of man and other animals has been found to contain a growth factor of protein nature, and chemical modifiers of its biological activity. The growth factor, in one of its two readily interconvertible forms, will support the growth and reproduction of nematodes in defined culture; the other form is without growth promoting activity in the cultures. Distinct materials have been separated from serum which either convert the growth factor into the activated form or prevent its conversion. These have been called activator and inhibitor, respectively. Although growth factor has growth promoting activity in tissue cells in culture as well as nematodes, nematodes provide the most convenient quantitative assay of growth factor and of its chemical state of activation. Its biological activity in all systems depends on which form it is in. Specific chemical interaction has been demonstrated between growth factor and its natural modifiers. The balance of physiological activator and inhibitor appears to regulate its biological effectiveness.
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