The document discusses nosodes in homeopathy. It defines nosodes as preparations made from microbes, viruses, fungi, or pathological secretions and excretions. Nosodes are classified into four types based on what they are derived from. The document lists several examples of specific nosodes like Psorinum, Tuberculinum, Variolinum, and others. It states that nosodes can be used when the best selected remedy fails to act, when there are few symptoms, or to address sequelae of infection.