How did medical understanding of diseases evolve between 1845 and 1945?

The correct answer highlights a significant shift in medical understanding during the period between 1845 and 1945, specifically the transition from humoral theory to germ theory of disease.

Humoral theory, which dated back to ancient Greece, posited that health was maintained by a balance of bodily fluids or 'humors': blood, phlegm, black bile, and yellow bile. This understanding largely influenced medical practices for centuries, affecting diagnosis, treatment, and the overall approach to health.

The germ theory of disease emerged in the late 19th century, spearheaded by scientists such as Louis Pasteur and Robert Koch. This theory established that many diseases were caused by microorganisms, which transformed the fundamental understanding of illness and its transmission. This shift not only provided a scientific basis for diagnosing and treating diseases but also led to major advancements in public health, hygiene practices, and the development of vaccines and antibiotics.

This evolution marked a critical turning point in medicine, leading to more effective treatments and a better understanding of infectious diseases, contrasting sharply with earlier beliefs centered on bodily imbalances. The other options do not accurately represent this significant change in medical understanding within the specified period.