BIOELECTRIC MEASUREMENTS I35 



and not in the cytoplasm. Later, chemical changes in the cytoplasm 

 become of profound importance, but it is doubtful whether or not 

 straightforward measurements of cytoplasmic conductivity will 

 produce information of great interest. In the case of the column 

 headed r.^ in Table 21, the values for the trout egg refer to the 

 globulin-containing solution within the vitelline membrane and 

 not to the cytoplasm, as in the other cases mentioned in this 

 Table. There is no cytoplasm to speak of in the unfertilized trout 



egg- 

 To summarize the contents of this chapter, measurements of 



bio-electric phenomena at fertilization have so far revealed little 

 of importance except for the increase in membrane capacitance 

 when sea-urchin eggs are fertilized. The main reason for this 

 unsatisfactory state of affairs is the refractory nature of the bio- 

 logical material and the associated technical difficulties. The 

 reader should consult Cole's papers for further details of experi- 

 ments involving alternating current measurements, while the 

 theory of such measurements when applied to eggs, and such 

 questions as the meaning of polarization capacitances, charac- 

 teristic frequencies, and the frequency-dependence of membrane 

 capacitances are summarized by Rothschild (1946). 



Note. Since this chapter was written, the results of new experi- 

 ments on the bioelectric properties of eggs have been published. 

 Although they do not in general affect my conclusions, they are 

 sufficiently important to deserve special mention. Grundfest et al. 

 (1955)* and Tyler et al. (1955)! observed a potential difference 

 of 30-60 mV. between the inside and the outside of the starfish 

 egg, the inside being negative. The p.d. could be reversibly re- 

 duced to zero by increasing the K content of the surrounding sea 

 water. The membrane resistance and capacitance were, respec- 

 tively, 2,000-3,000 ohm-cm^ and 0-5-1 -o /xF/cm^. The p.d. 

 decreased transiently at about the time of fertilization and, within 

 a minute of insemination, increased to 10-15 mV. above the "rest- 

 ing potential". 



* Grundfest, H., Kao, C. Y., Monroy, A. & Tyler, A. (1955) Biol. Bull., Wood's 

 Hole, 109, 346. 



t Tyler, A., Monroy, A., Kao, C. Y. & Grundfest, H. (1955) Biol. Bull., Wood's 

 Hole, 109, 352-353. 



K 



