RALPH S. LILLIE 137 



processes occurring at the surface of the metal. The parallelism of 

 these physical effects to the phenomena of electrotonus in irritable 

 Kving tissues is evident. Either facilitation or hindrance of the pro- 

 cesses of physiological activation and conduction may result by alter- 

 ing the electrical polarization of the cell surface through a constant 

 current, the effect varying according to the degree and orientation of 

 the polarizing influence; and the above experiments show that the 

 same is true of the film-covered metallic system. 



It is remarkable how closely the behavior of passive iron wires during 

 the period immediately following repassivation simulates that of 

 partially narcotized or asphyxiated nerves, or of nerves in which some 

 other kind of "block" is established. The "decrem.ent" type of 

 transmission characteristic of such wires is also shown by normal or 

 completely transmissive passive wires under certain special condi- 

 tions, e.g. in the neighborhood of a piece of platinum or other noble 

 metal in close contact with the wire. Such contact invariably retards 

 or prevents the passage of an activation wave started in another 

 region. The explanation of this interference is simple; platinum is 

 nobler in the electrochemical scale than passive iron; hence near the 

 contact there exists a local circuit in which the iron is anodal, a condi- 

 tion which, as already described, interferes with activation and trans- 

 mission. The following experiment will illustrate. If a piece of 

 platinum wire or foil is placed across the middle region of a passive 

 wire immersed in HNO3 (of 60 to 80 per cent) and pressed into close 

 contact by means of a glass rod, an activation wave started at one end 

 of the wire is typically blocked at the region of contact and fails to 

 enter the region beyond. The stoppage of the wave is not abrupt, 

 but occurs with a progressive retardation which is plainly visible at 

 a distance of 1 or 2 cm. from the contact. With an insufiiciently close 

 contact {i.e. too small a contact area) the block may not be com- 

 plete ; in such a case the activation wave is often observed to undergo 

 marked retardation^ — at times almost stopping — at the contact; but 

 after passing this region it regains its former speed, at first by a visible 

 acceleration, and travels in the usual manner to the end of the wire. 

 The parallel to a partial block in a nerve, due to local mechanical or 

 chemical treatment, is evident; in this case also there is retardation 

 in the altered region (or region of decrement), and, if the excitation 



