CHAP, i.] OF NUTRITION. 83 



liquid, impregnated as moreover it is with oxgyxm and carbonic 

 acid gas dissolved, that the histological elements choose the 

 materials which suit them and reject those which are no longer 

 suitable. At a more exalted degree of structure are superadded 

 special apparatus, systems more or less ramified with canals, in 

 which circulate the liquids and the gases. But even then the 

 interstitial, intercellular liquid ceases not to exist ; it merely 

 renews, revivifies, purifies itself without pause, seeking suste- 

 nance in the circulatory fluids, and ridding itself there, in its 

 turn, of the substances destined to elimination. 



In sum, the intercellular liquid acts toward the circulatory 

 fluids as the histological elements act toward itself. 



We see that it is by a peculiarity of construction that almost 

 all organised beings live in the air. In truth, all the histological 

 elements constituting the complex organisms are aquatic ; they 

 bathe in a special liquid, in a living medium, which is alike their 

 essential cause and the result of their nutritive activity. Cl. 

 Bernard has much contributed in these last years to propagate 

 this felicitous idea of the interior media, such as the blood of 

 animals, the sap of plants, and so on : "that ensemUe of all the 

 interstitial liquids, that expression of all the local nutritions, 

 that source and confluent alike of all elementary changes." 1 We 

 may admit, with the eminent physiologist, though with restric- 

 tions and exceptions for the living beings that are wholly rudi- 

 mentary, that there is no direct nutrition, and that, for instance, 

 the fragment of a fresh- water polypus, when it is reconstituted 

 and completed to the point of re-becoming an entire polypus, 

 avails itself principally of the nutritive interstitial fluid which 

 impregnated at the outset the separated fragment. " 



Thus, for every complex organised being there are three 

 superposed media, the cosmic medium, ae'rian, or aquatic but in 

 this last case holding the air in solution ; the sanguineous, or 

 sap-filled medium ; lastly, the interstitial, intercellular medium. 

 Naturally, the internal media need, like the external media, to 

 1 Revue Scientifique, 1874. 



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