Discovery of the Circulation of Blood
NOS: Theories are regarded as uncertain; William Harvey overturned theories developed by the ancient Greek philosopher Galen on movement of blood in the body
- A theory can be defined as:
- A carefully thought-out idea, with accompanying evidence, that explains observations of the natural world
- Theories are often constructed using the scientific method which involves bringing together many facts and hypotheses
- There is always a level of uncertainty when using scientific methods
- Uncertainty can be due to
- Natural variability of individual organisms
- Accuracy of measurements taken
- Theories can therefore be regarded as uncertain due to the uncertainties in the methods used
- New technology or the discovery of new evidence often results in theories being falsified or overturned
- An example of the falsification of a set of theories is that of Galen's theories about the blood and circulation
- Galen was an ancient Greek philosopher and surgeon who developed the following theories
- Blood is formed in the liver from ingested food
- Blood is pumped backwards and forwards between the liver and the right ventricle in the heart
- Some blood moves into the left ventricle through invisible pores and mixes with air from the lungs
- This mixing of air with blood produces spirits which are distributed to the body via the brain
- Blood is consumed by the tissues so that new blood must be continuously made
- Galen failed to present any evidence for his theories
- Galen was an ancient Greek philosopher and surgeon who developed the following theories
- Galen's theories were overturned by English physician William Harvey through a series of experiments and observations
- Harvey developed the following theories, which were ridiculed at the time
- Blood is pumped to the brain and body by the heart
- Blood circulates through the pulmonary and systemic circulation systems
- Capillaries exist which link arteries to veins
- Blood flow is too fast for blood to be consumed by the tissues; it would run out too quickly to be replaced. Instead, blood returns to the heart and re-circulates
- Harvey refused to accept Galen's theories without direct evidence and he toured Europe to demonstrate evidence for his own theories to others, eventually leading to acceptance of his new theories
- Harvey developed the following theories, which were ridiculed at the time
Galen proposed a model which was later disproved by William Harvey