100 THE NATURE AND ORIGIN OF LIFE 



expense protoplasm identical with its own. In such assimi- 

 lation there are two distinct phenomena. The protoplasm 

 fabricated is in reality identical with that which produces it, 

 both from the chemical point of view and from that of the 

 colloid or physical state. There are therefore in reality two 

 assimilations. One of them may be called physical or col- 

 loid assimilation ; it consists in setting up an equilibrium 

 between the colloid state of the living body and that of the 

 substances of its medium with which it is struggling. The 

 second is assimilation properly so called, or definitive, and is 

 probably subordinate to the first ; but it takes place only 

 within the limits of the living body itself, within its proto- 

 plasm, in a word. Physical assimilation, on the other hand, 

 when more or less advanced, may trench on the surrounding 

 medium. 



Thus what we call secretion of sucrase ~by yeast is only the 

 progressive influence of the colloid state of the function (Yeast 

 x Saccharose) on the medium containing the saccharose. 

 The different diastases secreted in a medium containing 

 various active substances by a living element A must be 

 colloid verifications of the partial functions (A x BJ, (A x 

 B 2 ), in which B t B 2 , . . ., are the different active substances 

 whose sum constitutes the totality B of exterior conditions. 

 To separate such diastases one from another amounts, there- 

 fore, to analysing the total function (A x B) into its partial 

 elements (A x B t ), (A x B 2 ), . . ., constituting an effective 

 analysis of the total vital activity of the species A under con- 

 ditions B. 



This remarkable physical assimilation has long been 

 known in certain particular cases under the name of digestion ; 

 but, as the properties of colloid bodies were unknown, diges- 

 tions were commonly looked on as dissolutions. For ex- 

 ample, meat digested by gastric juice was looked on as dis- 



