FIG. 1. Absolute movement in space of the skull and brain when the skull experi- 

 ences a linear acceleration. Arrows mark the actual paths in space of particles of 

 skull and brain. The brain participates completely in the motion, each bit being 

 pushed forward the requisite amount to keep step with the skull owing to the brain's 

 extreme incompressibility. No part of the brain moves appreciably relative to the 

 skull. Thus, the brain suffers no distortion and therefore no injury. 



FIG. 2. Absolute movement in space of a skull and hypothetical brain, supposed 

 completely incompressible and completely rigid, when the skull is rotated about o. 

 Arrows mark actual paths in space. The skull and brain move as a single rigid unit 

 and the brain is not distorted. 



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