Secrets of Growth

The annual $1,000 prize of the American Association for the Advancement of Science went this year to Zoology Professor Carrol Milton Williams of Harvard. His research* on the hormone system that makes the native silkworm (Cecropia) turn into a moth had nothing to do with silk production; it was aimed at the central secrets of growth and life.

Silkworms are fine subjects for the study of growth. Like most insects, they metamorphize, reorganizing nearly all of their body substance into new members and organs. Scattered through the mushy tissues of the big green caterpillars are small groups of cells (imaginal discs) that lie quiescent while the caterpillar is growing.

Wakening Discs. When the caterpillar is full-sized, its tissues dissolve to form a yolky fluid. The imaginal discs wake up suddenly. Nourished by the fluid, they burst into furious growth, constructing within the larva's old skin an entirely new insect: the hibernating pupa. Later, a similar burst of growth turns the pupa into the adult moth.

Working with radioactive tracers and delicate chemical tests, Dr. Williams and colleagues followed the progress of this two-stage wave of growth. It starts, they found, in a tiny group of 22 cells in the insect's brain. These generate a hormone that acts upon glands in the body, making them produce another hormone. This in turn causes certain cells to produce three enzymes (organic catalysts) that start the rapid growth of metamorphosis.

Sleeping Pupa.The three "cytochrome" enzymes are basic growth factors. Present in human beings as well as in silkworms, they control the utilization of oxygen in the tissues. Without them growth is impossible. The dormant Cecropia pupa contains no cytochrome enzymes. Therefore it cannot grow until they are provided by the chain of hormones that starts in its brain.

Silkworms are a long way from human problems, but Dr. Williams' work was largely supported by cancer research funds, because a cure for cancer may depend upon a better understanding of growth. Cancer cells grow lawlessly, defying the hormone controls that limit the growth of ordinary cells. By working out in detail the hormone system that governs the silkworm's metamorphosis. Dr. Williams has helped explain both lawful and lawless growth within the human body.

* With Assistants William Van der Kloot, Howard A. Schneidermann, Ned Feder, Dr. Richard C. Sanborn, Dr. Janet V. Passonneau and William H. Telfer.

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