432 



SCIENTIFIC THOUGHT. 



39. 

 The 



" internal 

 medium." 



it were the inner atmosphere which any large assembly 

 of living units must necessarily create for itself. All 

 larger organisms are complex societies of living units 

 which depend not only on the external but also on the 

 internal medium which bathes them. It was one of 

 Claude Bernard's happiest generalisations to look upon 

 the blood, not as a living tissue but as a means of com- 

 munication of the living tissues of the organism, as an 

 internal medium which bears the same relation to the 

 constituent tissues that the external medium, the 

 atmosphere, does to the whole body. 



One of the principal functions of this artificial medium 

 or atmosphere which the larger organisms possess, create 

 and maintain for themselves during their life, is to 

 enable a particular elementary substance to get access 

 to every living cell or tissue of the organism. This 

 substance is oxygen, without which the continuance 

 of life in the higher organisms seems impossible. 

 That life is a process of combustion is accordingly a 



possess " un milieu intericur per- 

 fectionue " (p. 104). But they 

 begin their existence as beings 

 with an oscillating life when they 

 are in the form of eggs. Of the vie 

 constante ou lihre Claude Bernard 

 says : " Je crois avoir le premier 

 insiste sur cette idee qu'il y a pour 

 I'animal reellement deux milieuxj; 

 un milieu exterieiir dans lequel est 

 place I'organisme, et un milieu 

 intcrieur dans lequel vivent les 

 Elements des tissus. L'existence 

 de I'etre se passe, non pas dans le 

 milieu exterieur, air atmospherique 

 pour I'etre aerien, eau douce ou 

 sal^e pour le.s animaux aquatiques, 

 mais dans le milieu liquidc in- 

 tcrieur forme par le liquide 



organique circulant qui entoure et 

 baigne tou.s les elements auatom- 

 iques des tissus ; c'est la lymphe 

 ou le plasma, la partie liquide du 

 sang qui chez les animaux superieurs, 

 penetre les tissus et constitue 

 I'ensemble de tous les liquides in- 

 terstitials, expression de toutes les 

 nutritions locales, source et con- 

 fluent de tous les echanges ele- 

 mentaires. Un organisme complexe 

 doit etre consider^ comme une 

 rdunion d'etrcs simples qui sont 

 les elements anatomiques et qui 

 vivent dans le milieu liquide in- 

 terieur. La fixitd du milieu in- 

 terieur est la condition de la vie 

 libre indepcndante " (p. 113). 



