34 PHYSIOLOGICAL CHEMISTRY 



stances tends to decrease the surface tension. Thus, in accord- 

 ance with Gibbs' principle the dissolved substance will tend to 

 collect or accumulate in the surface film, to concentrate on the 

 surfaces of the dissolved particles. This is adsorption. Of 

 course the adsorbed substance may combine chemically with 

 the material in colloidal form, and it may be held on by elec- 

 trical forces. Adsorption phenomena are without doubt of great 

 importance in the body. Much study is being expended upon 

 them at the present time. 



Imbibition. The swelling up of a substance like gelatin when 

 placed in water is called imbibition. The gelatin particle in- 

 creases greatly in size, but does not go into solution. This 

 process is important, as in this way cells take up water. The 

 extent to which imbibition will proceed is greatly influenced by 

 the presence of salts, acids, bases, etc. Salts usually repress 

 the swelling to a point below that which would be reached in 

 pure water. Acids affect it differently according to their con- 



N 

 centration. At about ^on t ^ ie o reat est swelling takes place. If 



the strength of the acid is less than this, the swelling will be 

 smaller than in pure water. In stronger acid, the swelling is 

 at first rapid, but it does not reach so great a final value as in 

 the concentration specified above. 



From the foregoing pages it will be evident that colloidal solu- 

 tions are of great interest in connection with the study of the 

 chemistry of the body. 



