23. Issuing thence again, certain twin channels, each enclosing its own current like a pipe, disperse air and blood (that the liquid substance may have free course when accompanied and lightened by the motion of the heated substance) in divers directions over the whole body, breaking at every part into countless branching channels; while as the two principles of the vital powers mingle together (that alike which disperses heat, and that which supplies moisture to all parts of the body), they make, as it were, a sort of compulsory contribution from the substance with which they deal to the supreme force in the vital economy.