STRUCTURES RESEMBLING ORGANIC GROWTHS. 157 



nerve fiber) as the advancing wave of excitation reaches and 

 passes that point. 1 In the case of these various vital phenomena 

 it seems highly probable, from the degee and nature of the 

 resemblances which they bear to the simple physico-chemical 

 phenomena described in this section, that the essential deter- 

 mining factors are also electrical currents between adjoining cells 

 or cell-regions. These, according to their direction, local den- 

 sity, and intensity, may initiate, inhibit, or reinforce processes 

 at various points along the path of the current. 



It may sometimes be desirable to demonstrate still further 

 the electrical nature of these inhibitory and accelerating in- 

 fluences. This may be done most readily by passing the current 

 from a battery, connected with a rheocord, through the ferri- 

 cyanide solution, using iron wire as electrodes. The formation 

 of filaments at the anode is promoted and at the cathode is 

 prevented, to a degree which varies with the potential between 

 the electrodes; this potential may be changed at wjll by shifting 

 the position of the slider. 



III. BIOLOGICAL COMPARISON. 



In comparing phenomena of the above described kind with 

 physiological phenomena it is obvious that careful distinction 

 must be made between resemblances that are superficial and 

 resemblances that are based upon a fundamental identity in the 

 nature of the determining conditions. It need scarcely be pointed 

 out that in the specific character of the structure-forming chem- 

 ical reactions there is no resemblance between the two processes 

 under comparison. The complex and imperfectly understood 

 metabolic transformations in living cells are of a kind entirely 

 different from the simple cross-decompositions and precipita- 

 tions of the above experiments. The resemblances relate to 

 the conditions under which the chemical reactions take place, to 

 the type of structure formed, and to the mode of transmission 

 of chemical influence from one region to another region which is 

 connected with the first only through the medium of an electric 

 conductor. Chemical action at a distance is a phenomenon 

 universally met with in organisms; and the attempts to explain 



1 Amer. Journ. Physiol., 1916, Vol. 41, see pp. I34~5- 



