150 THE ENGINES OF THE HUMAN BODY 



the chemical processes which take place during respiration 

 and combustion are identical. That was done by the 

 cleverest chemist and natural philosopher then in Europe 

 — Antoine Laurent Lavoisier. He was ten years younger 

 than Priestley and twelve younger than Cavendish, and 

 whilst they were circulating round the circumference of 

 the problem of respiration in England he went straight 

 to its centre in France. He proved that the same 

 chemical changes took place in the lungs as in a lighted 

 candle. " Fixed air," given off by both candle and lungs, 

 he showed to be produced by the union of definite pro- 

 portions of carbon and oxygen ; water, which was also 

 formed, he proved to result from the union of hydrogen 

 and oxygen. Combustion and respiration were, therefore, 

 processes of the same kind, processes in which hydrogen 

 and carbon united with oxygen. The lungs, in Lavoisier's 

 opinion, were furnaces by which the body was, not cooled, 

 but heated ; breathing was a means of bringing fresh 

 oxygen to the combustion chambers of the lungs. 



The conception which Lavoisier formed as to the use 

 of the lungs may be represented by a simple experiment. 

 In fig. 36 a rubber membrane has been tied over the 

 mouth of a large inverted glass funnel, so as to form a 

 movable diaphragm. On the upper surface of the rubber 

 diaphragm stands a lighted candle. Presently the candle, 

 exhausting the supply of oxygen within the funnel, begins 

 to go out. But if the diaphragm be gently worked, so 

 as to bring breaths of fresh air down the pipe of the 

 funnel and throw out breaths of burned gases, then the 

 flame revives, and may be kept alight until the candle 

 has burned down in its socket. Lavoisier conceived that 

 in the myriads of minute air sacs of the lungs a form of 

 combustion was going on not unlike that represented in 

 the inverted glass funnel. 



It took nearly fifty years more to make quite certain 

 that combustion chambers are not confined to the lungs, 

 but, as we have already seen, exist in every particle of the 

 living body. Every microscopic unit, every corpuscle of 

 the tissues, is really a furnace in which a peculiar kind 



