

2 RESPIRATION 



nerves was of course only a modification of the idea then current, 

 and elaborated by Descartes among others, that muscular con- 

 traction depends upon the "animal spirits" passing down the 

 supposed nerve tubules from the brain. This conception was ap- 

 parently confirmed by the effects of cutting or ligaturing nerves; 

 and Lower, 8 another Oxford physician, performed the striking 

 experiment of completely disturbing the action of the heart by a 

 ligature on the vagus nerve. He had stumbled upon inhibition 

 and misinterpreted it in favor of Mayow's theory. 



About the same time another significant observation was made 

 by Hooke, 4 the Secretary of the Royal Society. He found that 

 when the chest of an animal was opened so that the lungs col- 

 lapsed, it could be revived and kept alive by artificial respiration, 

 and, if holes were pricked in the lungs so that air could pass 

 through them, the animal could still be kept alive if a stream of 

 air was continuously blown through the lungs, although they did 

 not move. 



The foundations thus seemed to be laid of our present knowl- 

 edge of the physiology of breathing; but unfortunately the sig- 

 nificance of the discoveries made at Oxford was not appreciated, 

 and indeed the study of physiology and other branches of natural 

 science there was practically allowed to die out for the succeeding 

 two hundred years. 



The next important step in connection with respiration was 

 the discovery, about the middle of the eighteenth century, by 

 Joseph Black of Edinburgh, that "fixed air" (carbon dioxide) 

 which he had found to be liberated by acids from mild alkalies 

 (carbonates) is given off by the lungs in respiration. Priestley 

 discovered soon afterward that what, in accordance with Stahl's 

 phlogiston theory, he called "dephlogisticated air" (oxygen) dis- 

 appears both in ordinary combustion and in animal respiration, 

 while it is produced by green plants in sunlight. Lavoisier then 

 followed up Black's and Priestley's work by showing that in 

 combustion what he for the first time called oxygen combines 

 with carbon and other substances, and that carbon dioxide is 

 produced by the combination of carbon and oxygen, while water 

 is produced by the combination of hydrogen and oxygen. He and 

 Laplace 5 also showed that the carbon dioxide produced by an 

 animal is nearly equivalent to the oxygen consumed, and that 



"Lower, Tractatus de Corde, p. 86, 1669. 



4 Hooke, Phil. Trans., II, p. 539, 1667. Hooke had been assistant to Willis 

 and Boyle at Oxford. 



"Lavoisier and Laplace, Memoir es de I'Academie des Sciences, p. 337, 1780. 



