SECT. 5] 



IN ONTOGENESIS 



829 



vitro for some time. If the measurement is made three-quarters of 

 an hour after the removal of the cells from the body, a much higher 

 resistance is found than if it is made immediately after removal. 

 This augmentation in vitro she found to be due only to r, not to R 

 or p; in other words, to an increasing ionic membrane imperme- 

 ability. The cells do not vary in electrolyte-content, or in membrane 

 polarisation. The augmentation is stopped by cold, and is therefore 

 probably chemical; some tissues show it more intensely than others. 

 In the case of the embryo, the following results were obtained : 



Length 



of 

 embryo 



(cm.) 



3 

 5 

 6 

 8 

 Term 



Table 97. Electrical resistance of liver cells. 



r (ohms) at the time of 

 removal of the material 



Foetal 



909 

 1240 



1425 

 1 140 

 1252 



Maternal 



1457 

 i860 

 1071 

 1840 

 1233 



45 minutes 

 afterwards 



Foetal Maternal 



1453 

 1986 

 1756 

 1300 

 2602 



3702 

 4217 

 3590 

 3232 

 2790 



Percentage 

 augmentation 



Foetal 

 60 

 60 



24 



14 



108 



Maternal 



I2D 



Evidently the electrical resistance of the embryonic tissues does not 

 augment in vitro to the same extent as that of the maternal tissues, 

 at least until birth, by which time the two react very similarly. 

 Mendeleef concluded that there was a relation between decrease of 

 membrane permeability in vitro, and its absolute level in growing and 

 stationary tissues. 



Philippson's methods (much modified) have also been used by 

 Cole to determine the impedance of suspensions of eggs to various 

 frequencies of alternating current. Operating on the eggs of Arbacia 

 punctulata Cole found that before fertilisation the values of the im- 

 pedance for any given frequency were quite variable, and there were 

 similar variations in the average specific resistance of the ^gg at 

 both high and low frequencies. Immediately after fertilisation, how- 

 ever, these quantities became quite constant and did not change 

 noticeably thereafter. Cole did not regard the work of Gray and 

 of McClendon, mentioned above, as very satisfactory, for it was 

 done at low frequencies and in such conditions that almost all the 

 current would flow through the intercellular sea water. In this way 

 a very small change in the size of the eggs would cause a con- 

 siderable change in the overall conductivity. Cole concluded, for 



