96 THE HUMAN BODY. 



from the principles in the organism which are introduced into 

 it by digestion or respiration. 



Lavoisier was the first to demonstrate the absorption of 

 oxygen by respiration, and to show by experiment the analogy 

 existing between combustion and respiration. " Respiration," 

 said he, " is nothing but a slow combustion of carbon and 

 hydrogen, which resembles, iri every respect, that which takes 

 place in a lamp. ... In respiration, as in combustion, it 

 is the atmosphere that furnishes the oxygen. . . . But since, 

 in respiration, it is the substance of the animal itself, it is 

 the blood which furnishes the combustible, if animals do 

 not regularly repair by alimentation that which they lose by 

 respiration the oil in the lamp will soon be wanting, and the 

 animal will perish as the lamp will go out for the want of 

 nourishment." Most physiologists have admitted Lavoisier's 

 theory, and they consider respiration a slow combustion of 

 the materials of the blood by the oxygen of the atmosphere, 

 and as the source of animal heat. We have just seen that this 

 combustion takes place, not only in the lungs, but through- 

 out the whole extent of the organs where the arterial blood 

 carries the oxygen which presides over the phenomena of 

 nutrition, that is, over the assimilation of the elements of 

 which the blood is formed, and over the decomposition of 

 some of these principles of which certain parts only remain 

 in the system, while others return to be burned in the 

 capillaries of the lungs, or to be exhaled in the form of gas 

 or vapour of water. 



Some authors again do not admit that combustion takes 

 place in respiration, the phenomena of which, of quite a dif- 

 ferent order according to them, may be attributed to a reac- 

 tion induced by the contact of organized substances. The 

 decomposition and disassimilation of these are due to a series 

 of acts of which very little is known, and which are compared 

 to what has been termed by Berzelius u catalytic phenomena" 

 But we confine ourselves to a mention only of this doctrine, 

 which is not generally accepted. 



Mechanism of respiration. We have seen that respiration 

 is divided into two movements inspiration and expiration. 

 In inspiration, the diaphragm contracts and sinks down, push- 



