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JOHN MAYOW. 



1643-1679. 



TRACING the evolution of the story we come next to John 

 Mayow, who was born in London in 1643, where he died in 

 1679 " in the joyous neighbourhood of Covent Garden " at 

 thirty-six, having accomplished much during the all too brief span of 

 his existence. He took his degree in law, not in medicine, at Oxford. 

 His famous work is Tractatus de sale nitro-, et spiritu nitro-aereo, 

 de respiratione, respiratione foetus in utero et ovo, de motu musculari, et 

 spiritisms animalibus, de rhachitide. (Oxon. 1668.) 



He knew that the heart was muscular and that the blood was 

 forced out during systole, for " if the heart of an animal just killed be 

 filled with water, you excite a movement like that which takes place 

 in systole, the contents of the ventricle are forthwith ejected." 



The mechanism of the entrance of air to the lungs he quite 

 understands. Malpighi had already shown the structure of the lung. 

 Mayow gives a figure of a bladder placed in a pair of bellows, with 

 the mouth of the bladder communicating with the nozzle of the 

 bellows. When the bellows are expanded, air rushes in, and, when 

 compressed, air is forced out. He figures the intercostal muscles, and 

 ascribes the increase in capacity of the chest during inspiration to 

 the raising of the ribs and the descent of the diaphragm. Expiration 

 is a passive act. 



It is the chemical aspect of the question with which the name of 

 Mayow is linked, for he showed that it was not merely a portion of the 

 air which is necessary for combustion and for respiration, but a parti- 

 cular part — or constituent — of the air. He called it sal nitro-aereum or 

 spiritus nitro-aereus or igneo-aereus. It was, in fact, the gas we now 

 call oxygen, which as such was not discovered till more than a hundred 

 years afterwards. 



He refers to Boyle's experiments, which show that something in 

 the air is necessary for the burning of every flame. The air for him 

 was a compound body. The nitro-aereal spirit gave the air its power 

 of supporting flame, and it was this that the blood in its passage 

 through the lungs abstracted from the air. Like Boyle, he knew that, 

 after breathing in a closed space, the volume of air was diminished, 

 but Mayow appears to have been the first to estimate the amount. 

 He puts it at -j^. Hales later on put it ys to 3^. Lavoisier in 1777 

 gave the amount as ^ -. The older observers, still under the sway of 

 the physical investigations on the elater or spring of the air, explained 

 this diminution of volume by saying that the air has lost part of its 

 elasticity or its spring. A candle burned in a closed vessel over 



