What significant discovery was made by Karl Landsteiner in 1901?

Karl Landsteiner made a groundbreaking discovery in 1901 by identifying the existence of blood groups. This was a pivotal advancement in the field of medicine and transfusion science. Before his work, blood transfusions could be highly dangerous as the understanding of blood compatibility was minimal. Landsteiner's identification of different blood groups—namely A, B, AB, and O—allowed for safer blood transfusions by ensuring that compatible blood types were matched, significantly reducing the risk of transfusion reactions.

His work laid the foundation for modern blood transfusion practices and blood banking. This discovery not only improved surgical outcomes and emergency medicine but also has continued to be crucial in various medical settings where blood products are required. The significance of this discovery goes beyond mere classification; it formed a basis for later developments in immunohematology and the overall understanding of human blood.

The other options, while important in the history of medicine, do not relate to Landsteiner's work. For example, the production of penicillin was a major advancement made by Alexander Fleming in 1928, which revolutionized the treatment of bacterial infections. The nature of microbes was elucidated through the work of various scientists, including Louis Pasteur and Robert Koch, and the process of