CONDUCTIVITY AND RESISTANT POWERS OF PARTS OF CELL 97 



tive, for if a high resistance is interposed in the circuit and a stronger 

 battery used, the same strength of current may be obtained without the 

 small changes in the resistance of the filament being able to affect the 

 strength of the current perceptibly. When this is done a similar though less 

 pronounced difference between the currents required for a shock-stoppage 

 is usually, though not always, shown. Hence the readier response is not 

 solely due to an increased excitability, but also to the diminished resistance. 



The electrical conductivity of the different parts of the cell is certainly 

 not the same, the cell-wall when moist and uncuticularized, and the cell- 

 sap appearing to conduct best, and the protoplasm less readily. Hence in 

 long cells with a thin lining layer of protoplasm most of the current will 

 pass through the cell-sap, but in tissues' composed of rounded protoplasmic 

 cells relatively more of the current will pass through the cell-walls. The 

 cell as a whole appears to have a lower electrical resistance than the water 

 outside it. This may be shown by placing a glass tube containing tap- 

 water in circuit with a galvanometer, and deflecting through the circuit 

 a fraction of the current from a single cell. The galvanometer may show 

 little or no deflection, but if filaments of Nitella or Chara are placed across 

 the platinum electrodes in the glass tube a distinct deflection is shown, and 

 hence the external resistance in the circuit has been decreased. The same 

 can be shown by the Wheatstone bridge arrangement previously mentioned. 

 The fact that a pronounced electrolytic effect may be produced both upon 

 the cell-wall and upon the cell-sap, before streaming has ceased in the 

 protoplasm, points to a lesser conductivity in the latter. 



When a current is passed through a cell in which the nucleus is anchored 

 to the wall by threads of protoplasm, the threads and the nucleus are always 

 affected first. The threads become thicker and are retracted, while the 

 nucleus first swells strongly and then ultimately collapses and dies, although 

 streaming may in some cases continue for one to several hours if the current 

 is then removed. This may partly be due to the greater sensitivity of the 

 nucleus to electric currents, but is also probably due to the fact that since 

 it and the threads lie in the better-conducting cell-sap they are exposed to 

 more of the current and experience a greater electrolytic action than the 

 peripheral layer of protoplasm. That an inherent difference between the 

 resistant powers of the nucleus and cytoplasm does actually exist, can 

 however be shown by using cells (Elodea, Vallisneria, Urtica) in which the 

 nucleus usually lies in the peripheral cytoplasm. Here, also, the collapse 

 and death of the nucleus occur before the whole of the cytoplasm has been 

 fatally affected (turgor still present), or sometimes before streaming has 

 ceased. 



Klemm has shown that the endoplasmic (vacuolar) membrane fre- 

 quently bursts or collapses before the rest of the cytoplasm is killed, and 

 this may be due to its immediate contiguity with the better-conducting 



EWART H 



