From the 9th century to14th century, Salerno Medical College in southern Italy has been the center of European medicine. Modern medical historians have found many discussions about blood in the textbooks published by 1 1 Century Salerno Medical College. For example, when talking about the manifestations of anemia, including sallow complexion, exophthalmos, flat pulse and rapid pulse, patients often feel heavy, and sometimes they have headaches and dry tongue.

When Salerno medicine was flourishing, roger bacon, an English monk, was ahead of the times. He criticized scholasticism and proposed that science should be based on experience, and knowledge should be obtained naturally through observation, not from books. Roger bacon not only put forward a new viewpoint of studying nature, but also his research in optics led to the discovery of microscope. 1285, in a book about optics, he mentioned a mirror that can hold large and small objects. Although he didn't build a microscope himself, he foresaw this great invention.

Nearly 300 years after roger bacon put forward the concept of microscope, Zhan Sen, a Dutch glasses manufacturer, manufactured the first microscope in 1590.

1665, an Englishman Hooke made a compound microscope on the basis of Jenson. However, the original microscope still has many technical problems such as lens quality, light source and precise focusing device when observing tiny objects. Therefore, the early microscope was just an ornament of the upper-class family and a fashionable thing.

With the continuous improvement of microscope, scientists began to use it for biological observation. The first person to observe and describe red blood cells with a microscope was Swammerdam in Amsterdam, the Netherlands. "I observed the muscles, skin, eyes and blood of frogs," Swamodam wrote in the History of Insects published in 1658. When I put them under the microscope, I found that they are made up of smaller fibers and smaller balls ... "1660, Marby, an anatomist at the University of Bologna, Italy, observed the phenomenon that red blood cells of frogs flow through capillaries, proving the connection between arteries and veins.

As an amateur, Levin Hook of Delft, the Netherlands, is keen on observing with a microscope. He recorded his observation of human red blood cells in detail: "I have tried to observe blood many times, hoping to understand its composition." I collected some blood from my own hands and observed (under the microscope) that they were made up of many very small balls, but I'm not sure if all blood is like this. "He sent the record to the philosophical bulletin of the Royal Society of London. 1674 On September 2 1, this famous observation report was published in the Philosophical Bulletin of the Royal Society of London.

However, if Dr Graff, a friend of Levin Hook's, had not tried to publish a communication from the secretary of the Royal Society of London describing his microscopic observations, Levin Hook's research might have been forgotten. From today's perspective, it seems incredible that the famous scientific publication Philosophical Bulletin of the Royal Society of London published the observation results of a person without any scientific background. Of course, the Philosophical Bulletin of the Royal Society of London at that time was just published (published in 1665). In fact, the Philosophical Bulletin of the Royal Society of London at that time not only published many important scientific discoveries, but also mixed with some specious and even wrong observations and arguments.

The invention of the microscope ushered in a new era. 1675 In May, Spinoza mentioned in a letter to Henry Odenberg, secretary of the Royal Society that he and his friends thought the invention of the microscope was a surprise. The report in the September issue of Literature Monthly 1684 said: "After this news was published in the country where Levin Hook lived, many other countries also published the news that he invented the microscope, so this news is quite reliable. France, Britain and Germany; Newspapers in China are talking about his name and discoveries, so that he has become a famous figure all over the world. "

Of course, people still have doubts about how Levin Hook saw many subtle anatomical structures with his original microscope with only a magnifying glass. Some scholars believe that Levin Hooke may use glasses to combine with his microscope, so he created a compound microscope, which improved the magnification of the microscope and enabled him to observe the tiny anatomical structure of the human body. The microscope invented by Levin Hooke is now kept in the utrecht university Museum in the Netherlands.