Ehrlich was a German bacteriologist who was awarded the Nobel Prize in Physiology or Medicine in 1908 for his work on immunology. He is also noted for his work in hematology, cellular pathology, and the use of dyes in microscopy. Ehrlich coined the term “chemotherapy” and is credited with the first empirical observation of the blood-brain barrier. He also made notable contributions to the treatment of syphilis, stimulating research that led to the development of what widely-used drug? Discuss