438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
BLOCK OF CONDUCTION BY THE ACTION OF POISON. 
I have also succeeded in arresting conduction of excitation in 
plants by local application of poisonous drugs. The defect of 
Pfeffer’s experiment lay in his attempt to arrest the impulse by the 
application of a volatile anesthetic: like chloroform on a surface of 
a thick stem. The chloroform escapes in the form of vapor; the 
access of the solution under these conditions to the interior of the 
tissue by absorption can only be slight and therefore ineffective 
in arresting the excitatory impulse. It occurred -to me that the 
physiological block induced by a drug could be rendered more 
effective in two different ways: First, by the selection of a thin 
leaf stalk mstead of a thick stem for the purpose of the experiment, 
so that the access of 
the solution to the in- 
terior became less dif- 
ficult; in the second 
place by the employ- 
ment of strong non- 
volatile toxic agents, 
like solutions of cop- 
per sulphate or of 
potassium cyanide. 
The choice of astrong 
- poison was deemed 
Fic. 15.—Abolition of conduction by local application of potassium ~ advisable. because 
cyanide. (1) Normal record; (2) arrest of conduction after appli- ue 
cation for five minutes; (3) persistent abolition of conduction, even the absor ption of even 
when stimulus was increased fifteen-fold; (4) record of direct g gmall quan ti ty 
stimulation. : : 
might in such a case 
prove effective in abolishing the conducting power. My anticipations 
were fully justified. By the application of copper sulphate the con- 
ducting power was found arrested in the course of 20 minutes; 
but the more deadly cyanide solution abolished the conducting 
power in a period as short as five minutes. (Fig. 15.) 
Accounts have thus been given of some typical experiments by 
which the nervous impulse is discriminated from the mechanical 
impulse. It has been shown that excitation may be initiated and 
transmitted in the plant in the complete absence of any mechanical 
disturbance. It has been shown that the various conditions which 
accelerate, retard, or arrest the nervous impulse in the animal also 
enhance, retard, or block the impulse in the plant in a manner which 
is identical. I have, moreover, from my investigations on the plant 
nerve, led to the discovery of certain hitherto unknown characteristics 
of the animal nerve. The investigation on the simplest type of 
plant nerve is expected to cast a flood of light on the obscure phe- 
