Jeff Immelt, the chief executive officer of General Electric, showed off what he called the “stethoscope of the 21st century” at the Web 2.0 Summit today. As he did so, he held up a white gadget with a flip-out screen and a control mechanism that looks lot like the old iPod navigation wheels. Immelt said the device could do ultrasound scans on the fly and wirelessly communicate the data as necessary. Doctors can use the devices to immediately see, for instance, if an unborn baby is in a dang