What is the primary story used in Chapter 34 to illustrate the power of Udi?

Chapter 34 primarily focuses on the story of a doctor from Malegaon whose nephew was suffering from a severe and incurable disease called a bone-cyst (Hadyavran). As the chapter narrates, the doctor, along with other physicians and surgeons, had exhausted all native and foreign treatments, including surgery, with no success. The boy was in immense pain. As a last resort, the family heard about Sai Baba of Shirdi and traveled to see him. Upon hearing their plea, Sai Baba, the embodiment of compassion, reassured them and gave them Udi to apply to the wound, promising a cure. This story serves as a powerful, experience-based illustration of Udi's glory, as stated in the chapter's introduction.