We interpret the 15 equations of Kaluza-Klein gravity as 10 Einstein e
quations, 1 wave equation and 4 equations of motion. An exact cosmolog
ical solution of the apparently empty 5D field equations describes a 4
D fluid with an effective density and pressure induced by the curvatur
e associated with the fifth dimension. The rest mass of a particle in
the fluid depends on the global solution and changes slowly with time.
This approach to Kaluza-Klein theory in general results in Machian co
smologies.