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Britain in the XVII century

2) Harvey: discovering circulation

 

3 mental revolutions happened in the XVII century in England. Hobbes changed the views for state origination, Newton - for the reasons of motion. And now we will speak about William Harvey who changed the views of the motion of blood and a heart work. Not only the theory of medicine changed but also a practice. The new way of treatment appeared.

In order to understand what was the sense of Harvey’s discovery, it is necessary to imagine work of heart from the modern point of view.

Heart drives blood in two circles. Blood may be in two states: "pure" and "dirty". Pure contains oxygen and nutrients. Dirty - carbonic gas and products of an exchange (dross).

 

 

 

 

 

The Major circle goes from left to right. Pure blood flows to organs and tissue. There a metabolism takes place. Blood gives oxygen and nutrients, takes away carbonic gas and comes back into heart.

The Minor circle goes from right to left through lungs. There blood gives away carbonic gas, takes oxygen and comes back into heart.

The change of gases in tissue and lungs occurs through the walls of very small vessels - capillaries. Their walls let only one molecule to pass at any moment. The vessels are very small, but there are a lot of them. All the body is penetrated by capillaries. The whole length of all capillaries in a body of an adult man is equal to the length of Earth diameter (more than 40 thousand km). Capillaries can be seen only in a microscope. Heart is the pump which drives the blood in two closed circles.

What was thought about the work of heart before Harvey? For almost 2 thousand years the theory created by ancient Roman doctor Galen dominated in medicine. Galen created the theory saying, that blood was constantly originated and destroyed in body. It was formed of food.

What organ produced blood according to Galen? This concept has reflected in English, the name of this organ has derived from latin "life" - In a liver

According to Galen, from liver blood flows to heart. In heart it mixes with air. The blood rich with air, runs to different parts of body. Then it spoils, runs to arms and legs and is destroyed there.

 

 

 

This theory caused the main method of treatment – blood-letting. It was thought: ill person is a person with too much spoiled blood in his arms and legs. To help him meant to let the spoiled blood flow away. Sometimes blood-lettings helped, but rather often they killed people, especially children.

 

For almost 2000 years the theory existed saying blood to appear of food, mix with air in heart and disappear in arms and legs. It caused the blood-letting as the way of treatement.

 

In the XVI century several doctors began to hesitate about the correctness of Galen’s theory. For example, Italian doctor Fabricius discovered the existence of valves in venous . They let blood flow only in one direction. Fabricius did not know what it was necessary for. Because he did not know, that blood moved in a circle, and valves prevented its back movement. The enigma was solved by his pupil English doctor William Harvey. Solving of this created the new doctrine about heart and quite new methods of treatment.

William Harvey (1578-1657) was a son of a merchant. He had graduated from Cambridge, and then studied at the famous Renaissance physician Fabricius in Italy. There he got interested in the work of heart.

Having returned to England, he began to work at hospital in London. At the same time his private practice was so successful, that Harvey became the doctor of king. The main scientific problem for him was the work of heart and blood circulation. To understand the work of this system he had done hundreds of experiments on animals of 60 species. Charles I allowed Harvey to use his hunting lands for medical experiments. Harvey caught deers in a huge Windsor park and made the experiments with them.

In 30 years of work Harvey came to the next conclusions

1 - blood is not born and is not destroyed all the time, the same blood circulates in the closed cycle

2 – there is no air in the heart, it is a pump for blood only

3 - valves of venues are necessary not to allow blood flow back

How did Harvey come to the idea of the closed cycle?

The main proof of the closed blood circulation was the calculation of the quantity of the blood which was passing through heart. Harvey counted frequency of systoles and the total volume of blood in a body of a sheep. For 30 minutes the weight of blood equal to the weight of the animal should have passed through the heart. It was much more, than the food eaten by the sheep. Such a huge quantity of blood could not appear and disappear all the time. There was the only possible conclusion: blood circulates. It doesn’t appear and disappear. There were also the other proofs.

Harvey did not hasten to publish the results. His conclusions contradicted all then medical practice. He was afraid of general indignation. The book was published in 10 years after the discovery in Germany.

The indignation had followed. Doctors were divided into the supporters and opponents of Harvey. The opponents nicknamed Harvey «circulator». Blood circulation in Latin is circulatio, and «circulator» means "a deceiver". However in England Harvey’s discovery was recognized, not at once, but by the end of his life.

Harvey discovery caused a revolution in the ways of treatment. Letting out blood was recognized senseless and harmful. The idea of injections appeared. If blood circulates, the injected substance will reach a sore point. So the medical practice changed from bloodletting to injections.

 

Harvey proved:

1 - blood circulates in the closed cycle

2 – there is no air in the heart, it is a pump for blood only

Категория: Лекции по истории Англии | Добавил: Senebty (10.02.2018)
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