In our crossed circulation experiments we found that neither waste
products nor metabolic poisons could be considered the principal
cause of the brain-cell changes. We found that in the production
both of muscular action and of fever there were brain-cell changes
which showed a quantita-tive relation to the temperature changes
or to the muscular work done. We observed that under deep
morphinization the febrile response or the muscular work done was
either diminished or eliminated and that the brain-cell changes were
correspondingly diminished or eliminated. We found also that brain-cell
changes and muscular work followed electric stimulation alone.
I conclude, therefore, that the brain-cell changes are work changes.
We shall next consider other organs of the kinetic system in their
relation to muscular activity, to emotion, to consciousness,
to sleep, to hibernation, and to heat production.