Antidepressants Blog

Man has always been acquainted with blood. Inevitable wounds caused it to flow and the spurting from arteries showed that there was great pressure back of it. Yet it was not until the time of the Pilgrims’ coming to America that William Harvey showed how the blood was continually pumped by the heart through the arteries and returned by way of the veins.
Harvey was one of the great observers. Philosophers had said that the hen broke the egg open to free the chick. Harvey looked and found that the chick itself did the pecking open. After he had studied at Caius College, Cambridge, (pronounced “keys” and still the great training school for English physicians) he began to study the heart and blood vessels in men and animals. It was known that both arteries and veins were filled with blood, but it was thought that it just surged back and forth. Harvey studied the action of the heart; he saw that the valves prevented back flow; and he estimated the capacity of the heart and the rate of the flow. When he was through, there was no disputing his theory of the circulation.
During the English Civil War he was an intimate of Charles I and accompanied him on his campaigns. There is a pretty story of his sitting under a hedge at one battle reading a book to the royal children, the Prince of Wales and the Duke of York, until a cannon ball grazed the ground near them. Charles lost the war and was beheaded, but Harvey was not bothered by the Parliamentarians. He was evidently somewhat the type of his namesake of whom Samuel Johnson said, “If you call a dog Hervey, I shall love him.”
We must consider Harvey’s work all the more remarkable as we realize that he could not know or demonstrate part of the course of the blood. It was some years later that the microscope was perfected so that Malpighi could see and describe the capillaries. These are the minute vessels through which the blood gets from the arteries to the veins; they are so small that the red blood corpuscles have to go through single file. In the days of small distances we were impressed to learn that if all one’s capillaries were placed end to end they would reach two and a half times around the earth at the equator.
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Next tool is the observation of the development of cancers in people. Work on the location of cancers and where they spread was mainly carried out in the nineteenth and early twentieth centuries and this process of careful description of what happens to patients, allied to very detailed descriptions of the behaviour of tumours, can still contribute useful knowledge. There remains a role for the doctor or group of doctors who keep meticulous records of the findings with large numbers of patients and the outcome for each and every one of them. This kind of clinical science is important but probably has now contributed most of what it can to our knowledge of cancer.
The third kind of method which helps us understand cancer is the study of the development of cancers in communities and of the links between the cancers seen in communities and other features of life in those communities, This is the science of epidemiology and it has, in many ways, been the most revealing of all of the sciences in the study of cancer in chit century (although many scientists practising in the laboratory might not share this view). In fact, epidemiology and experimental science and clinical observation are all complementary and, together, can tell us much about the different causes of cancer.
The study of the development of cancers in populations is best illustrated by the link between lung cancer and smoking. This topic merits a chapter in its own right, which will follow later, but the essence of the observations allows us to illustrate how epidemiology can work. As smoking increased in communities in Western Europe and North America so did lung cancer. Within those communities, it seemed to be mainly people who smoked who got lung cancer. Different groups within the society who had different exposure to cigarette smoking had different rates of lung cancer and when particular groups, for instance doctors, reduced their smoking, lo and behold, they got less lung cancer. This is a simple statement of a very complicated story and the net result has been to reveal the single most important known cause of human cancer, cigarette smoke. All of these observations were made by studying the patterns of cancer within communities, although they went extended by experiments in which the important elements of cigarette smoke, particularly ear, were mixed with cells and were shown to be capable of causing cancerous changes. The link between cigarette smoking and lung cancer remains the strongest clearest and most important link in our entire knowledge of cancer, and the one that presents the greatest potential for winning the war against cancer, at least on that front. In other areas, the links between cancer and lifestyle are much less clear, but they may turn out to be even more important; they certainly require very careful study.
In this chapter we are going to explain how a researcher can work on these problems, how certain of the observations he makes may be very compelling and also what the pitfalls and uncertainties may be. This will provide the basis for discussing each of the important potential causes of cancer, one by one, in ensuing chapters. The values and the limitations of epidemiology are an extremely complex topic and are frequently only well understood by people who are deeply immersed in the subject professionally. Misunderstandings about the strengths and weaknesses of this science have generated considerable confusion among the general public and also among healthcare professionals, and it is worth spending some time looking at how the suggestions of epidemiology are studied and evaluated, how they become more certain and how they may well remain unproven despite many years of careful work.
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