i;r> EOOLOGI 



that lives, is a compound fluid. It is composed of, 1. Watery 



vapour, always proent in greater nr le>s quantities: and 

 '1. In 1(H) parts of pure atmospheric air : there an 90 of OXy- 

 ^en. "'. of a/.ote or nitrogen, with some trac.-> ot' carbonic 

 acid gas. Oft-repeated chemical f.xjH'riiiiciits have jirovcd 

 that it is the oxygen alone which maintains lite. The dis- 

 covery of this singular fact we owe (1777) to Lavoisier, a 

 celebrated French chemist, who was barbarously executed 

 during the French Revolution. 



118. By the action of respiration the oxygen is with- 

 drawn from the atmosphere, and disappears; in its place we 

 find carbonic acid gas; this gas is not respirahle, i.e., if 

 breathed it destroys life. In the consumption of oxygen and 

 the production of carbonic acid gas, respiration essentially 

 consists. 



119. Although azote or nitrogen IK- not a vital g. 

 presence in the atmosphere seems necessary to dilute the 

 oxygen ; and it has been observed, that a certain quantity of 

 a/ote is absorbed and given out in the act of respiration. 



120. Finally, there escapes with the fluids expired a 

 certain amount of vapour, which becomes conspicuous in cold 

 weather; this vapour is called pulmonary transpiration. 



121. It is whilst passing through the capillaries of the 

 lungs that the blood loses its dark venous hue. and becomes 

 of a bright vermilion arterial colour. Many experiments 

 have been made to prove that which seems obvious without 

 any. 



122. Theory of Rc^iraC,,,,,. What become* of the 

 oxygen which has disappeared, and what is the source of the 

 carbonic acid gas uniformly found as a product of respiration '? 

 The strong analogy existing between the phenomenon of 

 combustion, of a piece of charcoal for example, and respiration, 

 induced Lavoisier to conjecture them to be almost identical 

 processes; in both, the oxygen disappears, carbonic acid gas 

 is formed, and heat is disengaged. 



But this theory must be abandoned, as opposed to sub- 

 sequent experiments and fact>: carbonic acid ijas exists 

 a 1 reaily formed in the blood, and is simply exhaled from the 

 -urface of the vessels, whilst the oxygen is absorbed into 

 the blood, to be dissolved in it, and to bestow on its particles 

 their living qualities, characteristic of arterial blood. 



s' \'2'.\. A simple experiment, made by William Edwards, 

 .suilices tn place this matter in a clear light. Place in a close 



