The discovery of capillaries is attributed to the Italian physiologist Marcello Malpighi (1627-1694).
In 1660, observing with the microscope the lung of a frog, Malpighi noticed small blood vessels that connected the arteries with the veins. Being very thin vessels, Malpighi decided to call them capillaries, that is thin as a hair.
Today we know that the diameter of a hair is on average between 17 and 180 micrometers (there is a wide variability between people), while the diameter of a capillary measure on average from 5 to 10 micrometers.
The diameter of a capillary is therefore smaller than that of a hair.
