374 PROTOPLASMIC ACTION AND NERVOUS ACTION 



although the quantitative relations are different ; hitherto 

 these relations have been less completely investigated in 

 plants than in animals. Transmission of- excitation in 

 plants resembles that of slowly conducting animal 

 tissues,' and the excitation-process is accompanied by a 

 negative bioelectric variation. A prolonged refractory 

 period succeeds the motor response in Mimosa, and this 

 condition also appears to be general in plants. The 

 presence of a high degree of turgor in plant cells renders 

 the evidence of a temporary loss of semi-permeability 

 during excitation in many respects more definite and com- 

 plete than in the case of animal tissues ; but in other respects 

 the fundamental processes underlying stimulation appear 

 to be of the same kind in both groups of organisms. 



In the higher animals the phenomena accompanying 

 the secretion of gland cells, especially those under nervous 

 control, show many resemblances to those just described 

 for motile plant tissues. There is the same loss of water 

 and dissolved material from the cell, the same electro- 

 motor variation, and the same gradual recovery. The 

 variations in the permeability of the mammalian kidney 

 cells under the influence of fear, excitement, or other 

 abnormal emotional or nervous conditions also suggest 

 that in these cells stimulation is associated with increased 

 permeability; similar evidence is furnished by sweat 

 glands. The secretory phenomena accompanying fertili- 

 zation in many egg cells have already been mentioned. 



It might be objected that evidence drawn from the 

 observation of special tissues whose normal function 

 consists in the separation of dissolved substances, either 

 formed within the cells or collected from the surround- 



^ Cf. Bose, Proceedings of the Royal Society, B, XCIII (1922), 153. 



