34 PHYSICAL CHEMISTRY IN MEDICINE. 



is destined to contribute much toward an understanding 

 of biological problems. 



III. 



The sols also play an eminent part in life processes. 

 In contrast to the green plants, which, according to well- 

 known cultural experiments, are able to obtain their 

 nourishment from pure crystalloidal solutions, animals 

 are dependent upon liquid colloidal food. The process 

 of digestion serves to prepare nutrient sols capable of 

 absorption, and fluid colloids are mechanically moved 

 about and distributed throughout the organism to the 

 nourishing tissue fluids. While exerting only a slight 

 osmotic pressure, the dissolved colloids are nevertheless 

 able, through their inability to pass through animal 

 membranes, to exert a resorptive power, which through 

 a steady change in the osmotically active material, as 

 maintained by the circulation, finally attains significant 

 proportions (OKERBLOM). 



As recent investigations have shown, the sols have 

 several important properties in common with true sus- 

 pensions of very fine particles. The most important of 

 these from a biological standpoint is the at times enormous 

 surface effect of the colloidal particles contained in the 

 solution. BREDIG, who rediscovered the well-known 

 ferment-like action of metallic surfaces in the enormously 

 more active colloidal solutions of metals, and investigated 

 the whole subject quantitatively, has attempted to explain 

 the importance of the colloidal condition of the enzymes 

 by the enormous surface effects with which this condition 

 is combined. 



The free surface energy and the osmotic energy seem 



