Editing William Harvey (section)

== ''De Motu Cordis'' ==
{{more citations needed|section|date=March 2018}}<!--also, most of this content probably should go into the book article-->
{{Main|Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus}}
[[File:William Harvey ( 1578-1657) Venenbild.jpg|right|thumb|An experiment from Harvey's ''de Motu Cordis'']]

Published in 1628 in the city of [[Frankfurt]] (host to an [[Frankfurt Book Fair|annual book fair]] that Harvey knew would allow immediate dispersion of his work), the 72-page ''[[Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus]]'' contains the mature account of the [[pulmonary circulation|circulation of the blood]]. Opening with a dedication to King Charles I, the [[quarto]] has 17 chapters which give a clear and connected account of the action of the heart and the consequent movement of the blood around the body in a circuit. Having only a tiny lens at his disposal, Harvey was not able to reach the adequate pictures that were attained through such microscopes used by [[Antonie van Leeuwenhoek]]; thus he had to resort to theory {{en dash}} and not practical evidence {{en dash}} in certain parts of his book. After the first chapter, which simply outlines past ideas and accepted rules regarding the heart and lungs, Harvey moves on to a fundamental premise to his treatise, stating that it was important to study the heart when it was active in order to truly comprehend its true movement; a task which even he found of great difficulty, as he says:

<blockquote>
...I found the task so truly arduous... that I was almost tempted to think... that the movement of the heart was only to be comprehended by God. For I could neither rightly perceive at first when the [[Systole (medicine)|systole]] and when the [[diastole]] took place by reason of the rapidity of the movement...{{sfn|Power|1897|p=193}}
</blockquote>

This initial thought led Harvey's ambition and assiduousness to a detailed analysis of the overall structure of the heart (studied with fewer hindrances in cold-blooded animals). After this, Harvey analyses the [[artery|arteries]], showing how their pulsation depends upon the contraction of the [[left ventricle]], while the contraction of the [[right ventricle]] propels its charge of blood into the [[pulmonary artery]]. Whilst doing this, the physician reiterates the fact that these two [[Ventricle (heart)|ventricles]] move together almost simultaneously and not independently as had been thought previously by his predecessors. This discovery was made while observing the heart of such animals as the [[eel]] and several other types of fish; indeed, the general study of countless animals was of utmost importance to Harvey's research: among the ones already cited, one can add the study of the [[snail]], the [[invisible shrimp]], the [[chicken|chick]] before its hatching and even the pigeon. A digression to an experiment can be made to this note: using the inactive heart of a dead [[pigeon]] and placing upon it a finger wet with [[saliva]], Harvey was able to witness a transitory and yet incontrovertible pulsation. He had just witnessed the heart's ability to recover from [[Fatigue (medical)|fatigue]].<ref>{{cite book |author=Ashley, Euan A.|author2=Niebauer, Josef |chapter=Chapter 7, Heart failure |type= chapter text at website ncbi.nih.gov |title=Cardiology Explained |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK2218/ |publisher=Remedica |year=2004 }} [https://books.google.com/books?id=8MTPM9pwPAAC ''Cardiology Explained'' at books.google.com]</ref>
As early as the 17th century, William Harvey had already discerned the existence of the [[Ductus arteriosus]] and explained its relative function. Here he says, "...in [[embryo]]s, whilst the lungs are in a state of inaction, performing no function, subject to no movement any more than if they had not been present, Nature uses the two ventricles of the heart as if they formed but one for the transmission of the blood."{{sfn|Power|1897|pp=202–203}} However, the apex of Harvey's work is probably the eighth chapter, in which he deals with the actual quantity of blood passing through the heart from the [[vein]]s to the arteries. Coming into conflict with [[Galen]]'s accepted view of the [[liver]] as the origin of venous blood, Harvey estimated the capacity of the heart, how much blood is expelled through each [[Muscle contraction|pump]] of the heart, and the number of times the heart beats in a half an hour. All of these estimates were purposefully low, so that people could see the vast amount of blood Galen's theory required the liver to produce. He estimated that the capacity of the heart was {{convert|1.5|impfloz|ml|lk=on}}, and that every time the heart pumps, {{frac|8}} of that blood is expelled. This led to Harvey's estimate that about {{convert|1/6|impfloz|ml}} of blood went through the heart every time it pumped. The next estimate he used was that the heart beats 1,000 times every half an hour, which gave 10 pounds 6 ounces of blood in a half an hour, and when this number was multiplied by 48 half hours in a day he realised that the liver would have to produce 498 pounds of blood in a day, more than the weight of the whole body.

Having this simple but essential mathematical proportion at hand – which proved the overall impossible aforementioned role of the liver – Harvey went on to prove how the blood circulated in a circle by means of countless experiments initially done on [[snake|serpents]] and fish: tying their veins and arteries in separate periods of time, Harvey noticed the modifications which occurred; indeed, as he tied the veins, the heart would become empty, while as he did the same to the arteries, the organ would swell up.<ref>{{cite web |last1=Billimoria |first1=Aspi |title=Pioneers in Cardiology: William Harvey |url=https://www.japi.org/t284a4a4/william-harvey |website=JAPI}}</ref>

This process was later performed on the human body (in the image on the right): the physician tied a tight ligature onto the upper arm of a person. This would cut off blood flow from the arteries and the veins. When this was done, the arm below the [[ligature (medicine)|ligature]] was cool and pale, while above the ligature it was warm and swollen. The ligature was loosened slightly, which allowed blood from the arteries to come into the arm, since arteries are deeper in the flesh than the veins. When this was done, the opposite effect was seen in the lower arm. It was now warm and swollen. The veins were also more visible since now they were full of blood. Harvey then noticed little bumps in the veins, which he realised were the [[Vein valve|valves of the veins]] discovered by his teacher, [[Hieronymus Fabricius]]. Harvey tried to push blood in the vein down the arm, but to no avail. When he tried to push it up the arm, it moved quite easily. The same effect was seen in other veins of the body, except the veins in the neck. Those veins were different from the others – they did not allow blood to flow up, but only down. This led Harvey to believe that the veins allowed blood to flow to the heart, and the valves maintained the one-way flow.<ref>{{cite journal |last1=Friedland |first1=Gerald |title=Discovery of the function of the heart and circulation of blood |journal=Cardiovascular Journal of Africa |year=2009 |volume=20 |issue=3 |page=160 |pmid=19575077 |pmc=3721262 }}</ref>

Contrary to a popular misconception, Harvey did not predict the existence of [[capillary|capillaries]]. His observations convinced him that direct connection between veins and arteries are unnecessary; he wrote "blood permeates the pores" in the flesh and it is "absorbed and imbibed from every part" by the veins.<ref>As cited in: Douglas Allchin, "Pseudohistory and Pseudoscience", ''Science & Education'' 13: 179–195, 2004</ref>

Harvey's discovery of the circulation of the blood was based on inference, not direct observation, and was incompatible with the prevailing paradigm at the time.<ref name=":0" /> That paradigm held, among other things, that the blood could flow from one side of the heart to the other. Harvey knew that he was facing an uphill battle:

<blockquote>But what remains to be said about the quantity and source of the blood which thus passes, is of so novel and unheard-of character that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much doth want and custom, that become as another nature, and doctrine once sown and that hath struck deep root, and respect for antiquity, influence all men : still the die is cast, and my trust is in my love of truth, and the candour that inheres in cultivated minds.</blockquote>

Harvey's premonitions<ref>{{Cite book|title=The Sociology of Science |last=Barber|first=Bernard| chapter=Resistance by Scientists to Scientific Discovery| editor=W. Hirsch |publisher=New York: Free Press |year=1962 |page=555}}</ref> that his discovery would be met with scepticism, derision, and abuse, were entirely justified.<ref name=":0">{{Cite book|title=The art of scientific investigation|last=Beveridge|first=W. I. B.|publisher=W. W. Norton|year=1950|location=New York}}</ref> It took twenty years for his theory of the circulation of the blood to be generally accepted.