128 FERTILIZATION 



removal of calcium from sites in the nerve membrane (Franken- 

 haeuser & Hodgkin, 1955), and an outflow of potassium during 

 the falling or recovery phase. 



What evidence is there that anything like the phenomena de- 

 scribed in the preceding three paragraphs occurs at fertilization? 

 Dorfman claimed in 1934 that there was a potential difference of 

 44 mV. between the inside and outside of the unfertilized frog's 

 egg, the inside being negative, and that this potential difference 

 was reversed at fertilization. As, however, the insertion of a 

 needle or micro-electrode into an unfertilized frog's egg activates 

 the egg parthenogenetically, the potential changes observed by 

 Dorfman could have had little if anything to do with the early 

 phases of fertilization. Apart from this, the reversal of p.d. 

 took place one hour after insemination. In 1935, Hasama said 

 he had observed electrical changes in the egg of Hynobiiis nebu- 

 lostis (Schlegel) at fertilization. There is no reason to suppose 

 that Hasama's published records are anything but random base- 

 line fluctuations due to the measuring apparatus. A further claim 

 that activation of the frog's egg, both by a spermatozoon and by a 

 glass needle, is associated with electrical changes, was made in the 

 same year by Peterfi & Rothschild (1935). No records and very 

 few experimental details were published. When I systematically 

 repeated these experiments a year or so later, I came to the con- 

 clusion that though the puncture of an unfertilized frog's egg was 

 associated with electrical changes or signals which might be of 

 biological origin, the form of the changes was unpredictable and 

 the evidence that they were propagated over the egg surface in- 

 adequate. When, on the other hand, a frog's egg is fertilized, the 

 evidence that bio-electric changes occur is more convincing, 

 though such experiments present formidable technical difliculties; 

 but there is no reason to suppose that such changes are propagated 

 and to describe them as action potentials is wrong. Recent claims 

 that 'action potentials' occur when sea-urchin eggs are fertilized 

 (Scheer et al., 1954) are open to the same criticisms as the ex- 

 periments referred to above, which were done some twenty years 

 ago. The most we can say is that when eggs are fertilized, potential 

 changes of obscure origin are sometimes observed; but in the 

 absence of further evidence, these should not be called action 

 potentials, nor thought of as such. 



There are several reasons for thinking that these potential 



