Dr Henderson was a medical doctor who worked at Ashbridge Cottage Hospital. He took care of the Third Doctor during his stay at the hospital and was astounded by the Doctor's test results. He noted that the Doctor had a binary vascular system and an unidentifiable blood type.
When first seeing the Doctor's X-ray film, Henderson angrily assumed that someone in the radiography laboratory had created it as a prank on him. The tables were turned minutes later when Dr Lomax from the pathology department similarly accused Henderson of playing a practical joke by sending him non-human blood.
He was later knocked out by Channing who kidnapped the Doctor. When the Doctor was returned by Brigadier Lethbridge-Stewart in a coma, he told the Brigadier that the Doctor was in the deepest coma he'd ever scene. He later met with Dr Beavis, who intended to examine the Doctor, only to find the Doctor was gone. (TV: Spearhead from Space)