That is to say, the passage of a feeble current modi- fies conductivity for excitation in a selective manner. Con- ductivity is enhanced against, and diminished with, the direction of the current.
The miEiimura current which iuduces a perceptible cliange of conductivity varies somewhat in different specimens. The average value of this minimal current in autumn is 1'4 microamperes. The effect of even a feebler current may be detected by employing a test stimulus which is barely effective.
TABLE VI. — SHOWING KFFECTS OF UP-IIILL AND DOWN-HILL CURRENTS OF FEEBLE INTENSITY ON PERIOD OF TRANSMISSION THROUGH 15 MM.
| A table should appear at this position in the text. See Help:Table for formatting instructions. |
Number.
Intensitj' of current in
microamperes.
Period for up-hill
transmission.
Period for down-hill
transmission^
1 1-4
2 1-4
3 1 !•«
4 1-7
14 tenttis of a second
1'-'
16 tenths of a second
15 „ Arrest. 14 tenths of a second.
Having demonstrated the effect of direction of current on the velocity of transmission, I shall next describe other methods by which induced variations of conductivity may be exhibited.
DETERMINATION OF VARIATION OF CONDUCTIVITY BY METHOD OF MINIMAL STIMULUS AND RESPONSE.
In this method we employ a minimal stimulus, the transmitted effect of which under normal conditions gives rise to a feeble response. If the passage of a current in a given direction enhances conductivity, then the
