THE TRANSFERENCE OF STIMULI 183 



telephone, and that the results they call forth will depend at what point 

 and by whom they are received. 



After any irritable response all organisms strive to regain the original 

 condition of equilibrium, and the same is also the case under permanent 

 stimulation, except that a new condition of equilibrium is maintained as long 

 as the stimulus acts. Experiments upon plants have shown that irritable 

 impulses may travel from part to part without the existence of special nerves 

 as in animals. In spite of the fact that nerves, being specialized channels, 

 serve when irritated to call forth definite impulses, it is still unknown by 

 what means a stimulus is propagated in a nerve, for the electrical changes 

 which result from excitation may be merely the result of the chemical 

 changes involved. Even were this known it would be only one special mode 

 of conduction, and the various modes by which stimuli are transmitted 

 through protoplasm would still need to be discovered, for the protoplasmic 

 connexions may be regarded as the first stages in the differentiation of 

 special nerves. 



Anatomical investigations give no indication of the function of the interproto- 

 plasmic connexions, but the researches of Tovvnsend carried out at Pfeffer's 

 instigation have shown that certain stimulatory influences are transmitted through 

 the intercellular protoplasmic communications, and through the threads which may 

 connect the pieces of fragmented protoplasts 1 . Further researches in this direction 

 would undoubtedly reveal interesting facts as to the rate of propagation, the sphere 

 of influence, and so forth. 



The threads above mentioned all consist of ectoplasm, but stimuli emanating 

 from the nucleus or any endoplasmic organ must first traverse the endoplasm, 

 although they are not necessarily conducted equally well in all parts. It is in fact 

 possible that particular stimuli can only traverse special regions of the protoplast 

 or pass more readily in one direction than another. Furthermore, the conductivity 

 can undoubtedly be modified by the external conditions, and is also influenced by 

 the existent arrangement of parts and by functional exercise. 



When the nucleus is at one end of the cell, the influences radiating from it will 

 not reach all parts of the cytoplasm at the same time, independently of whether the 

 transference takes place through resting or streaming protoplasm. The velocity 

 and intensity with which a stimulus is transmitted along the long axis of a cell 

 may be favoured by the arrangement of the protoplasmic network, even when the 

 lining layer is also capable of conduction. Further, the absence or deficiency 

 of protoplasmic connexions in the side-walls of cells may cause a tissue to conduct 

 mainly or entirely in the longitudinal direction. Translocation, together with the 

 stimuli due to it, is in fact restricted in a similar manner to particular paths. 



Since the protoplasm often develops a fibrillar structure in connexion with 

 other tasks and functions, it is uncertain whether the systems of fibrillae observed 

 by Nemec in certain cases are specially adapted for the transmission of stimuli -. 



1 Townsend, Jahrb. f. wiss. Bot., 1897, Bd. xxx, p. 484. 



2 Nemec, Biol. Centralbl., 1900, Bd. xx, p. 369 ; Die Reizleitung und die reizleitenden Struktnren. 



