"Simplest Physiological Experiments"

William Harvey famously discovered the circulatory system – the flow of blood from heart to the various body parts, and back. A lot of discoveries in science needed the relevant equipment to be invented first (think of Galileo and the telescope), but not in Harvey’s case, writes Siddhartha Mukherjee in The Song of the Cell.

“He used the simplest physiological experiments to understand the workings of the heart.”

Let’s look at how Harvey went about it.

 

He punctured the arteries of animals when the blood had drained from them, “the veins were also eventually emptied of blood”. From this, he concluded that arteries and veins must be connected in a circuit.

 

When he pinched the aorta, the heart swelled up with blood. And when he pinched the main veins, the heart was drained of blood. This implied that arteries lead blood from the heart, and veins lead blood to the heart.

 

When Harvey examined the wall between the left and right side of the heart, he found it to be too thick, without any pores. Therefore, he realized, blood from the left side must travel to the lungs, before it entered the right side.

 

Lastly, when he watched the heart beating, he saw it contracting and relaxing. Proof that the heart was a pump that “sends blood in a circuit around the body”.

 

Most of these observation techniques seem so simple! Which is why Mukherjee wonders:

“It is unfathomable that it had eluded generations of physiologists.”