FACTS 155 



which constitute the life of each of these cellular bodies. 

 The collection of living cells draws from this interior medium 

 all its food substances Q and discharges into it all its ex- 

 crementitial substances R-. In general, the volume of the 

 interior medium is very restricted with respect to the total 

 volume of the living cells bathing in it. Consequently, the 

 elementary life manifested in the cells could not be much 

 prolonged unless the interior medium were renewed. 



Now the result of all these concomitant cellular activities 

 is shown by an activity of the whole multicellular being 

 an activity as a whole which should be called the life of 

 the multicellular being and has precisely for its effect to 

 renew the interior medium according to the needs of the 

 cells. We may even make of this renewal of the interior 

 medium an objective definition of the life of the multicellular 

 being. 



There is thus a double movement represented by the 

 arrows in Fig. 7 : 



1. A movement of ingress into the interior medium (nu- 

 trition, respiration), a movement of egress from the interior 

 medium to the exterior (excretion), and a brewing movement 

 of the entire interior medium (circulation). All this results 

 from the co-ordination of concomitant activities of the living 

 cells which constitute the multicellular being. 



2. Exchange movements between the interior medium 

 thus renewed and the various living cellular bodies P, 

 bathing in this interior medium. 



For example, in man oxygen enters into the blood through 

 the lungs and is carried by the blood to all the anatomical 

 elements, while the carbonic acid produced by these elements 

 is brought back to the lungs and excreted. The diagram of 

 Fig. 7 is as valid in the case of man as in that of the taenia 

 or pear-tree. 



