Heinrich Hermann Robert Koch was a researcher from Germany who studied the causative agents of infectious diseases in various parts of Europe, Africa, and Asia during the late nineteenth and early twentieth centuries. Koch developed what researchers call Koch’s postulates, which are four criteria designed to establish whether a bacterium causes a certain disease, and as of 2025, many researchers still use Koch’s postulates to guide their research. He also received the Nobel Prize in Physiology or Medicine for his discovery of Mycobacterium tuberculosis, which is the bacterium responsible for tuberculosis, an infectious disease that primarily attacks the lungs. Koch’s research on identifying disease-causing bacteria for various infectious diseases has advanced disease prevention and treatment, especially for tuberculosis, which has the ability to transmit from mother to child.

Non-therapeutic infant circumcision is the surgical removal of healthy foreskin from a male infant, often shortly after birth, for the purpose of achieving potential future medical benefits. Today, in 2025, the practice is common the United States but not as common in other Western industrialized countries. Though circumcision itself is an ancient cultural practice, doctors began performing circumcision for medical purposes only in the nineteenth century, and primarily in English-speaking countries. Orthopedic surgeon Lewis Sayre, who practiced medicine in New York City, New York, in the late nineteenth century popularized circumcision as a treatment for conditions such as muscle paralysis. Sayre’s ideas eventually fell out of favor, but doctors increasingly identified other reasons to perform the procedure, including the prevention of sexually transmitted diseases, urinary tract infections, and cancer. As of 2025, doctors, parents, ethicists, and others continue to debate the medical value of circumcision as well as the ethics of operating on the healthy genitals of people who cannot consent.