in the records exhibit chauged rates of conduction. The middle record is the normal, in the absence of any current. The upper record, denoted by the left-hand arrow, shows the action of a heterodromoas current in shortening the period of transmission and thus enhancing the velocity above the normal rate. The lower record, denoted by the right-hand arrow, exhibits the effect of a homodrom- ous current in retarding the velocity below the normal rate. I find thit a very feeble heterodromous current is enough to induce a considerable increase of velocity, which soon reaches a limit. For inducing retardation of velocity, a relatively strong homodromous current is necessary. I give below a table showing the results of several experiments.
TABLE V. — EFFECT OF HETERODROMOUS AND HOMODROMOUS CURRENT OF FEEBLE IXTEN'SITY OX VELOCITV OF TRANSMISSION.
| A table should appear at this position in the text. See Help:Table for formatting instructions. |
Speci- men.
iutengity of
heterodromous
current.
Acceleration
above normal
Intensity of
homodromous
current.
Retardation
below normal.
microampere
per cent
microamperes.
per cent.
1
0-35
16
I
20
2
0-7
13
1-5
19
3
0-8
18
2-0
14
4
0-8
11
20
13
5
10
18
2-5
12
6
lo
15
3-0
40
1
VARIATION OF INTENSITY OF TRANSMITTED EXCITATION UNDER HETERODROMOUS AND HOMODROMOUS CURRENTS.
In the next method of investigation, the induced varia- tion of intensity of transmitted excitation is inferred from the varying amplitude of response of the terminal muscle. Testing stimulus of sub-maximal intensity is applied at the middle of the nerve, v^^here the constant current induces no variation of excitability. Stimulation is eflEected either by single break-shock or by the summated effects of a definite number of equi-alternating shocks, or by chemical stimulation
