It is shown that mass density in matter originates as in Eq. (5) in the charge q sub F of fluid spacetime. Eq. (5) is written out in full in Eq. (11). This can be solved numerically by Horst Eckardt and Russ Davis. Eq. (11) shows that mass density induces a velocity field pattern in fluid spacetime. It is also shown through the wave equation (16) that mass density originates in the enthalpy or scalar potential of fluid spacetime. Conversely, material mass density induces enthalpy (a kind of energy) in spacetime. These inferences are rigorous logical deductions of ECE2 unified field theory. Eq. (16) can also be solved numerically by Horst Eckardt and Russ Davis, using their previous discussions.