24 P^TM'LASMIC ACTION AND NERVOUS ACTION 



imyorMfft because it furnishes the conditions for another 

 4^h^ characteristic group of properties, those dependent 

 ^fej^isferface conditions. The protoplasm is thus enabled 

 ^P rta utilize (so to speak) the special physical properties 

 ^.exhibited by matter at boundary surfaces. With fine 

 subdivision the proportion of surface protoplasm to the 

 total mass of living substance is large, and the role of 

 surface processes assumes corresponding importance. 

 This general point of view recalls Herbert Spencer's 

 explanation of cell-division as essentially a regulative 

 process, the effect of which is to maintain a certain 

 minimal surface-volume ratio in the protoplasmic mass. 

 The living substance enters into relation with its sur- 

 roundings through the intermediary of a surface layer, 

 which has special physiological properties, in corre- 

 spondence with the special nature of the physical condi- 

 tions resident at boundary surfaces. Evidence will be 

 presented later indicating that these electrical, adsorp- 

 tive, and catalytic properties of the protoplasmic 

 surface layers determine many of the most characteristic 

 features of protoplasmic activity, especially the automatic 

 and rhythmical processes, the susceptibility to electrical 

 influence, and the v^arious manifestations of irritability. 



