A 19-year-old Madison man accused of causing life-threatening injuries to his infant son last week is set to go on trial.  James Johnson pleaded not guilty plea to a charge of first-degree reckless injury during a Wednesday hearing. Prosecutors say officers responded to Johnson’s apartment in Madison April 4th after receiving a report of a baby having a seizure. Officers found damage to two walls in the bedroom of the home, and one appeared to have a hair embedded in it.  Investigators say after doctors determined the baby’s injuries were non-accidental, a child-abuse pediatrician examined the boy. The doctor found two complex skull fractures and three rib fractures that appeared to be more than 10 days old. Investigators say Johnson admitted hitting the baby with his fists multiple times.