ORIGIN OF THE FIRST ORGANISMS 385 



developed those properties of the system which may be 

 regarded as the characteristic features of life, which are 

 fundamental to the organisation of this form of the motion 

 of matter. 



The interaction with the external medium of such systems 

 as coacervate droplets, which have no organised network of 

 chemical reactions, can only be based on the permeability 

 of surface membranes or the adsorptive properties of colloids. 

 In this case, however, the entry of substances into the system 

 by such means soon ceases and the system enters into equi- 

 librium. Only when the substances entering the system in 

 one ^vay or another can be changed and accumulated within 

 the system in the form of some particular compounds, or cast 

 out into the surrounding medium as breakdown products, 

 can the phenomenon of interaction between the system and 

 its environment continue for a long time. This must have 

 occurred when coacervate drops were transformed into open 

 systems at a comparatively early stage in the evolution of the 

 original colloidal formations. But, in this case, the entry 

 of substances into the system or their expulsion into the 

 external medium must already have ceased to depend on 

 the simple laws of permeability and adsorption and have 

 depended on the state of development of the organisation of 

 the network of reactions into which the substances derived 

 from the external medium entered, or in which the break- 

 down products which were expelled were formed. 



It is precisely this sort of interaction with the external 

 medium, though in a considerably more highly developed 

 form, which is characteristic of all contemporary living 

 things. According to the evidence of contemporary cytology 

 and cellular physiology,^' the entry of substances from the 

 environment into the cell is not a passive process determined 

 by the greater or lesser mobility of these substances through 

 a hypothetical semi-permeable membrane, or by their selec- 

 tive adsorption on protoplasmic surfaces, as had earlier been 

 supposed. This entry is brought about by the active participa- 

 tion of the whole cellular metabolism. It occurs because 

 the substances which enter are drawn into the network of 

 metabolic reactions. For this reason any disturbance of meta- 

 bolism, such as a decrease in cellular respiration, has an 



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