36 



INJURY, RECOVERY, AND DEATH 



In order to ascertain the conductivity of the cell sap 

 of Nitella small amounts were expressed (see page 212) 

 and allowed to fill a capillary tube. Platinum electrodes 

 were then inserted into the opposite ends of the tube, 

 care being taken to exclude air bubbles. 



By means of these methods a variety of plant and 

 animal material has been studied by the writer. 18 Cer- 



FIG. 12. Apparatus for measuring the conductivity of Nitella. The cells, N, are placed in 

 a trough in a block of paraffin, P, and covered with plate glass, G. The solution is 

 poured in through the funnel, T, and runs out through the opening, O. At E and E are 



platinum electrodes. 



tain precautions have been observed in the choice of 

 material. It is desirable that the intercellular space 

 or substance shall be constant in amount. This is the 

 case in tissues, such as those of Laminaria, where the 

 cell walls are of a firm consistency and do not change 

 during the experiment. 19 On the other hand many 

 flowering plants present difficulties, since the spaces 

 between the cells are largely filled with gas, which is 



18 Cf. Osterhout (1919, A, C). 



18 Plasmolysis must be avoided since this increases the space between 

 the protoplasmic masses. 



