When masturbating, is it harmful to the body to cum over and over for hours? is having more than 10 at a time a bad thing?

Hard to say!: I would think that many of my colleagues would agree that your are over doing it a bit. The penis may revolt if you continue this as will the prostate, testicles and the urethra. It would appear you have an obsession and perhaps a neurosis regarding masturbation. I would recommend you to cut this activity back to 1-2 times a day by will power and see what happens. Otherwise see your doctor.