"selecting" spheres out of a grid

Hi,

I've got a 3d grid of spheres and some curves which go through the grid. I want to "select" only the Spheres which are intersected by the Curves. I tried it with different Intersections but i can't manage to do it. 

I would be happy if someone could give me a quick advice on how to achive that. Thank you!

Greetings,

Johnny