1750: Purpose of air, breathing is learned

Stephen Hales (1677-1761) 

So we are now in the year 1750 sitting among a group of fellow students at the University of Glasgow. The topic for today, says our instructor in his usual monotone manor, is the purpose of air.

He reminds us that in 1553, Michael Servetus was the first to speculate that it was the lungs that caused dark blood to become bright red, and not the heart.

In 1640, he says, William Harvey was the first to describe the systemic circulation of the blood through the vessels of the body.

In 1667, Joachim Becher published a book, "Physical Education," in which he said the four classic elements of fire, earth, air and water were no longer relevant, and replaced them with three earth forms: terra lapidea, terra fluida, and terra pinguis.  He believed terra pinguis was responsible for combustion and rusting.

Joseph Black (1728-1799)

In 1697 George Ernst Stahl changed this theory slightly and used the term phligoston (Greek term for burning up) to describe a material or principle of fire (not the fire itself) that was released into the air during combustion.  When a substance was burned, the combustible components of the burned material were released into the air, thus causing it to become impure.

This theory, says our instructor, is the generally accepted theory of today. However, it must be known that another theory, that substances are formed from atoms, that is beginning to be more generally accepted in our time.  However, before we get to that discussion let's continue our history.

In 1668, John Mayow was the first to speculate that the purpose of the lungs was not to cool the heart, but for the exchange of gases.  He believed a substance in the air -- nitro-aerial gas -- was inhaled into the lungs, and when it entered the blood stream the blood turned from a dark color to a bright red.  This, he speculated, was why venous blood was dark and arterial blood red.

He also speculated that a vapor produced by the blood was exhaled by the lungs. He did not know that nitro-aerial gas was oxygen, and he did not know that the substance produced by the blood and exhaled by the lungs was carbon dioxide. He may have made these discoveries had he not died at the young age of 35, before any of his works were published.

In 1727 and 1733 Stephen Hales published the results of experiments on air and respiration where he proved that there is no circulatory system in trees like there is in humans and animals.  (2, page 193)

So, by 1750, our present year, investigators had determined that one of these gases was fixed air that was exhaled by the lungs, and the other was a vapor that was inhaled by the lungs.

One of the students in our class is Joesph Black.  He would go on to become the first to recognize that this gas was burned off during the exhalation phase of respiration.   He discovered it "was deadly to animals, and could distinguish a flame." (1) (2, page 193-194)

References:

1. "Carbon Dioxide,"  Scienceclariied.com, http://www.scienceclarified.com/Ca-Ch/Carbon-Dioxide.html#b, observed the site on May 4, 2012 (this information is available at a variety of sources, although I chose to give sciencedaily.com credit)
2. Magner, Lois N., "History of Life Sciences," 2002, 3rd edition, New York, Marcel Dekker

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