Cancer
In the 1890s, French scientists discovered radioactive decay.  Radiation therapy became the first cancer treatment that worked and did not involve surgery.  It required a new multi-disciplinary approach to cancer treatment (people doing different jobs were working together to treat patients).  The surgeon was no longer working by himself - he worked together with hospital radiologists (people who gave and read X-rays) to help patients.  This team approach meant changes in how they worked.  The different people on the team had to communicate with each other and work together, which they were not used to doing.  It also meant that treatment had to be done in a hospital rather than at the patient's home.  Because of this, patients' information had to be put together into files kept at the hospital (called "medical records"). Because this information was now being kept and written down, scientists were able to do the first statistical patient studies using numbers to study questions like how many people who have a certain type of cancer or get a certain treatment survive.