Secret of Growth

One of science's deepest mysteries is what makes living creatures grow and what makes most of them stop growing as they reach maturity. In Nature, Professor Carroll M. Williams of Harvard describes research that may cast light on this basic mystery. He has extracted from mammalian tissues a "golden oil" that, injected into a caterpillar, stops its development and prevents its transformation into a butterfly.

Biologists guessed a generation ago that the metamorphosis of insects (changing from larvae to pupae and from pupae to adults) is probably controlled by a chemical hormone. Three years ago Dr. Williams extracted an oil from the abdomens of silkworm moths, injected it into silkworm pupae. It stopped their normal development. The pupae never became adult moths, instead developed into a second kind of pupa. Smaller doses brought forth monstrosities with mingled patches of adult and juvenile tissue. Williams concluded that the oil contained a "juvenile hormone."

After Williams' discovery, other biologists ransacked nature looking for the presence of the juvenile hormone in other species. Last year Drs. Lawrence I. Gilbert and Howard A. Schneiderman of Cornell University extracted a substance from the cortex of the adrenal glands of cattle. They found it had the same effect on silkworm pupae as the moth hormone. For the first time a hormone extracted from vertebrates was shown to influence the growth of invertebrate insects.

Pursuing the search, Physiologist Williams found a substance apparently identical with the juvenile hormone in nearly every animal material from tenderloin steak to the human placenta. The richest source in any mammal seems to be the thymus gland, which is believed to control growth. Significantly, Williams found no trace of his golden oil in any vegetable.

The juvenile hormone may prove to be a substance that controls growth in mammals as well as insects. But so far Dr. Williams has not isolated the pure hormone or determined its chemical character, points out that its presence in mammalian tissues may be only a biochemical curiosity.

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