In “Parasites: A Treatise on the Entozoa of Man and Animals. Including Some Account of the Ectozoa,” T. Spencer Cobbold offers a comprehensive examination of parasitic organisms, exploring their morphology, life cycles, and taxonomy with meticulous detail. Written in the late 19th century, this treatise is characterized by its empirical observations and scientific rigor, reflecting the burgeoning field of parasitology during a period when microbiology was coming into its own. Cobbold's insightful commentary juxtaposes meticulous descriptions of entozoa'Äîorganisms living within their hosts'Äîwith discussions on ectozoa, highlighting the complexities of host-parasite interactions and the implications for both human and animal health. The book serves not only as a scientific reference but also as a snapshot of the period's scientific exploration and curiosity about the natural world. T. Spencer Cobbold was a prominent figure in the realm of veterinary medicine and parasitology, which greatly informed his writings. His extensive experience studying parasites in various hosts allowed him to approach the subject with both practical and theoretical insight. Cobbold'Äôs commitment to understanding the ecological and pathological roles of parasites was driven by a broader interest in how these organisms impact health and disease, an interest that would become foundational to the field of medical and veterinary parasitology. This seminal work is highly recommended for scholars, students, and practitioners interested in the intricate world of parasites. Cobbold'Äôs meticulous observations and thorough classifications provide an invaluable resource, fostering a deeper appreciation for the complexities of parasitic life. By illuminating the often-overlooked relationships between hosts and parasites, this treatise remains a vital foundation for understanding parasitology today.