PROTOPLASM AS A PHYSICAL SYSTEM 63 



dependent chiefly on surface effects, of which two classes 

 appear to be especially important from the biological 

 point of view: (i) adsorption effects, leading to increased 

 concentration at surfaces and hence increased reaction- 

 velocity; and (2) electrolytic effects, due to the existence 

 of local potential differences between different regions of 

 the surface separating the two phases; when both phases 

 conduct electricity, local circuits may thus arise, furnish- 

 ing the conditions for electrolysis. This latter effect may 

 also be regarded as a form of catalysis, and is illustrated 

 in the spreading of rust spots on iron surfaces, or the 

 periodic catalysis of H2O2 by mercury. Both kinds of 

 effects are of fundamental importance in protoplasmic 

 processes, as will be shown in more detail later. Other 

 conditions characteristic of surfaces may also enter 

 (see pp. 217 ff.). 



As already pointed out, all forms of protoplasm 

 exhibit the power of specific synthesis characteristic of 

 life. The constructive metabolism by which the specific 

 structural elements are built up and maintained must, 

 like other forms of metabolism, be under the control of 

 structure. This synthetic activity, being a universal 

 property of living matter, is undoubtedly to be correlated 

 with the most general or fundamental type of structure 

 exhibited by protoplasm. In correspondence with its 

 uniformity of essential chemical composition and chemical 

 behavior, protoplasm must also possess a uniformity in 

 its essential type of physical structure; underlying the 

 variety of structural detail must be some characteristic 

 type of structural composition common to all forms of 

 protoplasm, and determining the special features of its 

 chemical activity. The traditional problem of the 



