It is possible for a man to hold to a book of medicine and say, "I have no need of a doctor; I will act according to the book; in it every disease is named, all symptoms are explained, the diagnosis of each ailment is completely written out, and a prescription for each malady is furnished; therefore, why do I need a doctor?" This is sheer ignorance. A physician is needed to prescribe. Through his skill the principles of the book are correctly and effectively applied until the patient is restored to health.