Whales Don't Get the Bends

What is a whale's spout made of? One theory: the spout is condensed vapor from the whale's moist breath. But in the tropics, where breath does not condense, the whale's spout is just as visible as in arctic cold. In Britain's Nature, Dr. F. C. Fraser and P. E. Purves tackle the old controversy again.

The Fraser-Purves theory: the spout is foam (mucus, gas and globules of emulsified oil) that forms in the whale's lungs. When the whale surfaces after a dive and empties its lungs, the foam expelled is the visible spout.

When a human diver descends to great depths, the nitrogen in his lungs tends to dissolve in his blood. When he comes to the surface, it forms bubbles that clog the circulation. This might not happen to whales if their lungs were full of oily foam. Oil has an affinity for nitrogen; it can absorb six times as much as blood can. Fraser & Purves think that when a whale dives, the nitrogen in the air of its lungs is absorbed by oil droplets before it gets into the blood. So the whale makes a deep dive and surfaces without suffering the bends.

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