Ignaz Semmelweis was a Hungarian physician who introduced hand-washing into medical practice after observing women in an obstetrics ward during his training. At the time, childbed fever (puerperal fever) was a common disease in maternity wards and was generally seen as incurable and inevitable. However, in 1847, Semmelweis noticed that the women in the portion of the clinic treated by midwives had much lower rates of childbed fever than those who were treated by medical students. He theorized that the medical students carried something to the women they examined, possibly from the dissecting room. He then ordered the students to wash their hands in a chlorinated lime solution before examining each patient. The mortality rate of the student treated women dropped from 18.27% to 1.27%. Initially, other physicians, especially older physicians, rejected the idea and childbed fever continued to rage in maternity wards across Europe. In 1861, Semmelweis published his tretise, The Etiology, Concept, and Prophylaxis of Childbed Fever. He died at 47 in 1865 of childbed fever after cutting his hand during an operation.

As the 19th century progressed, his discovery was accepted and put into practice all across the world, resulting in millions of lives being saved. He was not the first person to discover the importance of handwashing in medicine, but it was his book that ultimately popularized the practice. 

While this occurred before Sen was born, an understanding of the importance of antiseptic practices are vital to a modern understanding of medicine. From her memoir, it is unclear whether they were taught to practice handwashing and other sterilization techniques. Especially given that quite a bit of Sen's medical practice focused on obstetrics, this discovery would likely be very important in her practice. 

SOURCES

https://www.britannica.com/biography/Ignaz-Semmelweis

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6333090/

https://www.washingtonpost.com/nation/2020/03/23/ignaz-semmelweis-handwashing-coronavirus/

https://www.npr.org/sections/health-shots/2015/01/12/375663920/the-docto...