Who is Dr. Humphreys from Perelandra and what is their importance?

Ransom instructs the narrator to bring Dr. Humphreys to him when the time comes for him to return to earth. Ransom is unsure what his physical condition will be when he returns..... or if indeed he will return at all. Humphreys accompanies the narrator to Ransom's home to help rescue him and nurse him back to health. The only injury he has to treat is a hemorrhage on Ransom's heel.