126 BIOLOGY. [Book ii. 



rejects all the aerian azote, and, in addition, a certain portion in 

 excess, arising from the reduction of the aliments.^ 



Oxygen has a very different part to play in the exercise of 

 physiological functions. It penetrates into the blood, is con- 

 veyed by it into contact with the tissues which impregnate 

 themselves with it, and burn, thanks to its assistance, the 

 imme'diate principles which constitute them, particularly the 

 complex organic substances. Finally, the anatomical elements 

 in return restore to the sanguineous medium an equal volume 

 of carbonic acid, of which a large portion is exhaled, particularly 

 through the respiratory sui'faces, a. smaller part forming alkaline 

 carbonates, by combining itself with the bases previously existing 

 in the tissues. 



This oxydation of anatomical elements is one of the primordial 

 phenomena of life. It must take place, under pain of death, in 

 every living substance, figurate or amorphous, vegetal or animal. 

 It is a fundamental, biological phenomenon, and all the reactions 

 of living chemistry depend upon it. Without its intervention, 

 there can no longer be either assimilation or dis-assimilation in 

 any organized substance, and the anatomical elements become 

 incapable of exercising their special functions ; the chlorophyllian 

 cell then ceases its chemical synthesis, the muscular animal 

 fibre no longer contracts, the- nervous cell becomes incapable of 

 feeling, volition, or thought ; there is no longer either maintenance, 

 or development, or generation of the anatomical elements. 



Amongst the invertebrated animals, whose blood does not 

 contain globules, it is the sangmneous plasma itself which 

 conveys the dissolved; oxygen to the tissues. Amongst almost 

 the whole of the vertebrates, on the contrary, this office principally 

 devolves upon the red sanguineous globules, as we have already! 

 indicated. The substance of these globules, which has a great 

 affinity for oxygen, imbibes it, fixes many volumes of it, and 

 becomes vermilion. The oxygen thus flowing on with the 



' Ch. Eotiu, Ses Humeurs. 



