PHYSICAL FORCES INVOLVED IN BIOLOGICAL ACTIVITIES 183 



microscope which are designated in size by the term amicrons. Accord- 

 ing to Zsigmondy the size of the particles covered in colloids ranges 



a O 



1 



FIG. ioga. Arrangement of ultramicroscope. (After Bayliss.} 



FIG. 1096. Rays of light in ultramicroscope. (After Bayliss.} 



from o.i/-t to 

 cules : 



Ostwald gives the estimated sizes of certain mole- 



Hydrogen gas ................................... 0.067-0.157^ 



Water vapor .................................... 0.113^ 



Carbon dioxide ........................ .......... o . 285^ 



Sodium chloride .................................. o . 26^ju 



Sugar ........................................... o . 7/j.fj. 



Some conception of the size of molecules and colloidal particles, 

 although they may not be absolute and even subject to great range or 

 variability, contributes to an understanding of colloidal and molecular 

 solutions, osmotic action, life-activities, lower limits of size of micro- 

 organisms and other natural phenomena. 



The "disperse phase" of colloidal solutions suggests at once the 

 extensive surface made possible by the particles in suspension and must 

 likewise suggest the extent of surface energy present in the form of 

 surface tension and adsorption. These factors are largely involved in 



