Pasteurized milk that has gone sour
Is half a gallon of milk that you may not need to throw out worth getting food poisoning over? If I had to choose between possible bloody diarrhea, vomiting, severe pain, seizures and possibly even death and spending a few more dollars, I certainly would spend a few more dollars.

Throw the stuff away. If it's gone sour, you have a lively colony of bacteria in there.

They may or may not be harmful, but I cannot stress enough that it's simply too dangerous to try.