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The Body Electric

A natural voltage within a growing embryo may teach it left from right

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7:36pm, September 14, 2003

As anyone who has ever recited the Pledge of Allegiance will attest, having your heart in the right place means having it on your left side. Despite the outward symmetry of the human body, left-right differences abound beneath everyone's skin. The majority of the heart's bulk usually sits on the body's left side, although the organ's aorta loops to the right. The right lung has three lobes, while the left has two. The liver and gallbladder fill up the right side of the abdomen, whereas the spleen and stomach dominate the left.

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