240 RALPH S. LILLIE AND EARL N. JOHNSTON. 



conditions exhibit similar behavior. It should further be noted 

 that this behavior is itself a factor in the determination of the 

 type of structure formed. The structure of the system and its 

 physical activity thus mutually influence each other, and the 

 eventual outcome in permanent structure deposited is the result 

 of this continual interplay of chemical and physical factors. 



The whole sequence of events in the formation of a single 

 striated precipitation-vesicle of cadmium ferricyanide may be 

 briefly sketched as follows (for further details see below, page 

 260). The original vesicle or tubule with which growth starts 

 is formed at an anodal region on the surface of the metal; here 

 cadmium ions enter solution and interact w r ith ferricyanide 

 anions to form cadmium ferricyanide, which is deposited as a 

 thin easily ruptured semipermeable precipitation-membrane. 

 The interior of this original precipitation-vesicle contains a 

 soluble salt of the metal (e. g., CdCl2, formed from soluble chloride 

 in the solution), and more precipitate is formed wherever the 

 wall of the vesicle ruptures and the solution flows out from the 

 interior to meet the potassium ferricyanide outside. The direc- 

 tion and rate of this outflow depend upon various physical 

 factors (form and size of vesicle, character of local circuit, external 

 conditions, etc.), which consequently determine where and at 

 what rate new precipitation-structure is formed. The physical 

 properties of the newly deposited precipitation-membrane, which 

 by degrees builds up the wall of the growing vesicle, depend 

 upon the specific chemical nature of the precipitate (since to a 

 definite chemical composition correspond definite physical 

 properties) ; these determine the properties of the wall of the 

 vesicle, e. g., its elasticity, coherence and resistance to rupture, 

 and hence the rate of the rhythmical rupture; this again deter- 

 mines the rhythm in the outflow of solution, and consequently 

 the rhythm of precipitation; and this latter rhythm determines 

 the arrangement and spacing of the striations, i. e., the character- 

 istic morphological features of the completed structure. 



This whole sequence may serve as a simplified model or epi- 

 tome of what takes place in any organic formative process. In 

 both the living system land its inorganic model the energy for 

 the work of growth is derived from the energy freed in chemical 



