  We prove that an indecomposable principally polarized abelian variety $X$ is
the Jacobain of a curve if and only if there exist vectors $U\neq 0,V$ such
that the roots $x_i(y)$ of the theta-functional equation $\theta(Ux+Vy+Z)=0$
satisfy the equations of motion of the {\it formal infinite-dimensional
Calogero-Moser system}
