ABSTRACT
Of all the sciences, medicine surely has the most direct and immediate impact on people's lives. The twentieth-century saw immense improvements in peoples' overall levels of health, especially in the Western world. One of the greatest scientific achievements of the late nineteenth century was the discovery of germs, living organisms too small to be seen by any but the most powerful microscopes, which are the main cause of infectious diseases. Blood transfusion is not a new practice. The Incas in Peru were doing it in the sixteenth century when they were discovered by the Spanish conquistadors. By the beginning of the twentieth-century, it was already known that any animal's diet needed three major components: proteins, fats and carbohydrates. Further, proteins were already known to be compounded from simpler substances called amino acids. Diabetes mellitus has been a well-known condition ever since the seventeenth century.
