October 14, 1921] 



SCIENCE 



361 



gists. Lillie's independent rediscovery of 

 this analogy, however, and his detailed studies 

 and analysis strengthen the probahility of a 

 fundamental relation subsisting between the 

 two phenomena. 



The passage of the wave of activation over 

 the surface of a short wire is so rapid, that 

 it is not easily demonstrated to a large group 

 of students. The simple arrangement here 

 described is clearly visible at a considerable 

 distance and has been used successfully as a 

 lecture table demonstration. 



Nine and a half meters of a ten-meter piece 

 of number 20 piano wire are wound by hand 

 on a machine lathe into a spring small enough 

 to slip easily into a 100 c.c. burette. After 

 stretching the spring sufficiently to insulate 

 the individual turns, a glass tube is inserted 

 in the spring and the remaining half meter 

 of wire is returned through this tube. When 



set into the burette the upper end of this tube 

 should just reach the burette top (Fig. 1). 

 The two free ends of the piano wire are now 

 connected through thin iron- wires with a 

 demonstration galvanometer or voltmeter 

 which registers both positive and negative 

 variations. After filling the burette three 

 quarters with 70 per cent. c.p. nitric acid 

 (by volume) the spring coil is lowered into it 

 until about an inch of the lower end of the 

 coil is submerged in the acid. The submerged 

 inch of wire immediately begins to dissolve 

 but if the coil is held in this position until 

 chemical action ceases, the entire wire may 

 be lowered into the acid without further 

 action. In other words by passifying one end 

 of a wire and then slowly lowering the re- 

 mainder of that wire into acid the entire 

 piece is passified. To prevent activation the 

 wire must be lowered slowly and steadily. 

 The coil is now ready to be tested at intervals 

 with a zinc or copper " stimulus " applied 

 just at the surface of the nitric acid at the 

 top of the burette. After a somewhat variable 

 latent period the entire spring becomes 

 activated. The wave of activation passes 

 down the coil and back through the return 

 wire registering a diphasic " action current " 

 on the galvanometer. 



In its passage down the spring the activa- 

 tion wave sets free a shower of minute bub- 

 bles which change the color of the acid suf- 

 ficiently to make the wave of activity clearly 

 visible even at some distance from the prepar- 

 ation. This preparation recovers rapidly at 

 room temperature and may be used repeated- 

 ly to demonstrate mechanical, chemical and 

 electrical stimulation as well as the time re- 

 quired for the passage of a single activation 

 wave over a distance of ten meters. At the 

 close of the demonstration the coil should be 

 removed from the burette, thoroughly rinsed 

 in slightly alkine water and alcohol and 

 rubbed briskly with a rough cloth. With 

 these precautions it may be used repeatedly. 

 Eeynold a. Spaeth 



The Physiological Laboratory, 



School op Hygiene and Public Health, 

 Johns Hopkins University 



