CHAPTER XY. 



OF THE RESPIRATORY ORGANS IN THE ANIMAL KINGDOM. 



THE fundamental phenomenon of respiration is very simple : 

 it is merely the exchange of the carbonic acid and the water 

 contained in an organism for the aerian oxygen. It is a 

 physical phenomenon governed in its ensemble by the laws of 

 osmosis. In respiration, the water which escapes from the 

 organised body is in the state of vapour. But the carbonic acid 

 expulsed results from the oxydation of the organised substance ; 

 consequently respiration is very intimately related to nutrition. 

 It has for object to ventilate the organism, to renew the air of 

 the interior medium. As there is no nutrition without absorp- 

 tion of oxygen, respiration is a primordial function ; it is effected 

 as an essential act of every living substance. It has been 

 objected to the generality of this law that certain infusoria, for 

 instance, certain vibrions, and so on, can live in a medium 

 charged with carbonic acid and destitute of oxygen. The excep- 

 tion cannot be admitted without solid proofs which are still 

 lacking. Of these pretended animalcules some are provided 

 with chlorophyll, and are rather to be regarded as plants. If 

 the statement were true for the others we should simply have to 

 conclude that they have the faculty of taking their oxygen from 

 the carbonic acid itself, by decomposing it. The whole organised 

 world absorbs oxygen and needs to absorb it. Not without 

 reason the ancients made synonyms of the verbs to breathe and 

 to live. Every organised being, vegetal or animal, dies more or 



