Many guys have used alcohol injections but what I want to know is how does work?

Once it's injected into the testicle what does the alcohol actually do to the testicle?

As said in your post a few people have done this.

I would suggest you read through this thread.

http://forums.eunuch.org/showthread.php ... yl+alcohol

Long story short, the alcohol injection idea came around from veterinary research into a serum for castration via injections. It was found that alcohol injected into a testicle caused sufficient cellular apoptosis to cause neutering in lab rats. Once this conclusion was reached, it naturally went on from there to here.