826 



BIOPHYSICAL PHENOMENA 



[PT. Ill 



of a tissue or of a whole organism increases with age. Whether this 

 has any relation to the salt- or ash-content will be discussed later, 

 but Gayda's figures for electrical resistance in Fig. 202 should cer- 

 tainly be compared with the figures for salt-content of frog embryos 

 and tadpoles obtained in the work of Schaper, and plotted in Fig. 230. 



Gayda 



© Resistance 

 ® 



10 20 30 



Days from fertilisation 



Fig. 202. 



The time relations are astonishingly concordant, for, whereas ac- 

 cording to Gayda the electrical resistance rises steadily until the 

 1 6th day from fertilisation, so according to Schaper the ash-content 

 falls steadily until the i6th day after fertilisation. After that point 

 the ash-content slowly rises again, and conversely the electrical 

 resistance slowly falls, or remains constant. In Fig. 202, the 

 potential difference between head and tail end of the embryos in 

 volts and amperes should be observed, passing steadily upward ou 



