EVOLUTION OF COLLOIDS 147 



these ferments which produce union and 

 reduplication within the living cells, are 

 exactly the same substances which digest and 

 break up the food when they are thrown out 

 by the digestive glands into the alimentary 

 canal, and so form soluble matter capable of 

 absorption. 



The food must be broken down into chemical 

 building stones from which the animal can 

 rebuild its own special and very specific 

 colloidal structures, which vary from one 

 species of animal to another. This chemical 

 detachment is achieved by means of soluble 

 ferments, or enzymes, discharged by the cells 

 of the digestive glands. In dilute solution 

 these attack the starches, fats, and proteins, 

 reversing the building up processes described 

 in the previous chapter. The smaller mole- 

 cules so formed are taken up into the body 

 and reach the cells. They undergo local 

 concentration in the cells, and these being 

 brought again in contact with exactly the same 

 ferments, also locally concentrated on surfaces, 

 exactly the opposite effect occurs, and the 

 building back into multi-molecules com- 

 mences. In dilute solution there is breaking 

 up, in concentrated solution there is con- 

 densation and re-duplication. It is only 

 when chemical unions are feeble and small 



