YIKES!!!!!
Let me see how to word this with the same sensitivity as used in your post.
Ask yourself this question:
"What would YOU do if YOU had a "blood sac hanging from your butt"?
The general consensus is treat your animals as you would yourself. Just because they cannot talk , they still can feel every bit of pain we can.
So PLEASE , as has been suggested see a vet ASAP
CML
Hi, this needs to be addressed by a vet ASAP. From your description, it sounds like rectal prolapse. Check out this link for more info.
www.petmd.com/cat/conditions/digestive/c_ct_rectal_prolapse
Get him to a vet as soon as possible, this is not something you can treat at home off internet advice.