Introduction:
The discovery of blood circulation in human beings is credited to William Harvey, an English physician, who made this groundbreaking observation in the early 17th century. His findings revolutionized the understanding of the circulatory system and laid the foundation for modern physiology.

William Harvey's Contribution:
William Harvey conducted extensive research and experiments to understand how blood circulates in the human body. His observations and experiments led him to propose the theory of blood circulation, which challenged the prevailing beliefs at that time.

Observations:
Harvey made several key observations that supported his theory of blood circulation:
1. The heart acts as a pump: He observed that the heart continuously pumps blood throughout the body, indicating that it plays a central role in circulation.
2. Blood flows in one direction: Harvey noticed that blood flows in one direction through the veins and arteries and does not reverse its course.
3. Blood volume remains constant: He observed that the volume of blood in the body remains relatively constant, suggesting that blood circulates in a closed system.

Experiments:
To support his observations, Harvey conducted various experiments, including:
1. Ligature experiments: He tied ligatures at different points along the veins and arteries of animals, demonstrating that blood flow is obstructed beyond the ligature.
2. Dissection experiments: Harvey dissected animals and observed the valves in veins, which allow blood to flow in one direction.
3. Pulse experiments: He measured the pulse rate and observed that it corresponds to the heart's contractions, further supporting his theory of blood circulation.

Publication and Impact:
In 1628, William Harvey published his findings in the book "De Motu Cordis" (On the Motion of the Heart and Blood), where he presented his theory of blood circulation. This publication received significant attention and laid the foundation for modern understanding of the circulatory system.

Conclusion:
In conclusion, William Harvey's extensive research, observations, and experiments led to the discovery of blood circulation in human beings. His work challenged existing beliefs and revolutionized the understanding of the circulatory system. Harvey's discovery remains a crucial milestone in the field of physiology and has had a profound impact on medical science.