THE CONQUEST OF DISEASE 



that the trees are his allies. Priestley was a 

 great chemist who loved his fellow men as 

 strongly as he loved the truth. A Birmingham 

 mob, urged on by the clergy of the Church of 

 England, wrecked his house, destroyed his 

 valuable library, scientific instruments, notes 

 and papers, attempted his life, and drove him 

 into exile. 



Then Lavoisier discovered that respiration 

 is characterized by the absorption of oxygen 

 and the exhalation of carbon dioxid. Animals 

 absorb out of the air oxygen, they exhale into 

 the air carbon dioxid ; plants absorb out of the 

 air carbon dioxid, they exhale into it oxygen. 

 Animals inhale oxygen, combine it with the 

 carbon of their tissues and food, and exhale 

 from their lungs carbon dioxid gas. The 

 trees absorb the carbon dioxid from the air 

 through their leaves, appropriate the carbon to 

 their structures, and throw off the oxygen. 

 Each requires what is a waste product of the 

 other. 



Borelli ( 1679) gave the first accurate account 

 of the mechanism of respiration. The chemis- 

 try of respiration could only be known after 

 the study of the gases involved. Joseph Black 

 in 1757 discovered carbon dioxid in the expired 



36 



