ITS SCOPE AND METHOD 61 



of ceaseless chemical action ; and in the animal body 

 chemical changes which evolve heat are exother- 

 mic immensely preponderate in the total chemical 

 activity. Closely bound up with the warmth of the 

 body is ' respiration'. Now so cardinal are chemical 

 data regarding the living body for the science of Phy- 

 siology that physiological search actually foreran the 

 course of purely chemical inquiry in regard to the 

 nature of air. It discovered in air the all-important 

 element oxygen a century before that element was 

 otherwise discovered. It did so by investigating respira- 

 tion. Mayow by his physiological experiments here in 

 Oxford in 1674 showed air until then accepted as a 

 homogeneous entity, the second of the four natural ele- 

 ments of the ancients to be a mixture of two aerial 

 substances, one of them (that later known as oxygen) 

 retained by animals in breathing and an essential support 

 to life. Mayow also showed that it is this same aerial com- 

 ponent which supports a flame in burning. He showed 

 that both the animal in living and the flame in burning 

 return to the air, in place of the component they remove, 

 a third gaseous substance heavier than that, a substance 

 unfit to support the flame or life, indeed on the contrary 

 nocuous to animal life. 



A century later the stupendous work of Lavoisier 

 founded modern chemistry. Then it became clear that 

 at the bottom of the lungs the blood as it streams past 

 takes oxygen from the air. The fish in river and sea 

 also take oxygen, drawing upon the relatively scant 

 quantity of that gas dissolved in such water. But our 

 blood and theirs take more than they can hold in mere 

 solution. Minute globules suspended in the fluid of the 

 blood have power in virtue of an iron-containing pig- 

 ment to seize the oxygen and hold it chemically. 



