[PyMOL] cut protein in half

 
 
Dear pymol users,
I want to make a cross-section on a ion tunnel protein to cut it in half and observe the intenal characters of the tunnel. According to materials on web, I runed the following commands:
hide all
show surface
set ray_trace_mode, 0
set two_sided_lighting, off
set ray_interior_color, grey50
 
But I didn't see any obvious change on the structure except that the protein became dim. Could you help me with that?
Tnanks in advance!
 
Yeping Sun