i 3 2 SEVENTEENTH CENTURY. PT. in. 



two gases. The one which he called fire-air was oxygen, 

 which was not known to other chemists for more than one 

 hundred years later, and the other and lighter one is now 

 called nitrogen. 



Having now proved that an animal in breathing uses up 

 the same part of the air which a candle does in burning, 

 Mayow wanted next to know what this fire-air did inside the 

 animal. Harvey, as you remember, had proved that the 

 blood passes through the lungs and there meets the air which 

 we draw in at each breath. Here then, said Mayow, the 

 fire-air particles must come in contact with the blood, and, 

 joining with it in the same way as they do with the fat of a 

 candle, must cause the heat of the blood. If any one wants 

 to prove this let him run fast. He will find that he is 

 obliged to breath more quickly and draw more air into his 

 lungs, which will soon make his blood hotter and move 

 more quickly, till his whole body glows with warmth. But 

 if this mixture of the air with the blood does really take 

 place, the arteries into which blood has just flowed from the 

 lungs and heart ought to be full of air ; and this is easily 

 proved to be the case by putting warm arterial blood under 

 an air-pump, where as soon as the pressure of the outside 

 air is taken off, innumerable bubbles rise out of the blood 

 as fast as they can come. 



In this way, by careful experiments and reasoning, Mayow 

 succeeded in proving that fire-air (or oxygen) is the chief 

 agent in combustion and respiration. If he had not died so 

 young he might have become more known, and men might 

 have studied his discoveries, which he published in 1674. 

 Unfortunately, however, he did not live to spread his know- 

 ledge, and a false theory of combustion caused his work to 

 be forgotten for many a long year. 



Theory of ' Phlogiston,' 1680-1723. This theory was 



