VARIATION OF POLAR REACTION 273 



efficiency of Ab is greater than Am ; under modification it 

 may become (a) equal to, or (b) less efficient than, Am. 



Modified Response Km Am 



The existence of modification (a) with the vanishing of 

 Km Ab has already been demonstrated. We next come 

 to the theoretical possibility of a modified type Km Am. 

 As already stated, in certain circumstances, especially late 



Fig. 129 — Polar reactions, Km, Km Am, Km Am Ab, under gradually 

 increasing current. 



in the season and in older specimens, I have not infrequently 

 met with this type. A series of records are reproduced in 

 fig. 129, in three cycles of effects of increasing current. In 

 these the acting e.m.f. was increased from 6 to 8 volts and 

 then to 10 volts. It will be seen that the stage Km Ab has 

 apparently vanished, its place being taken by Km Am. 

 An account of results obtained with four different specimens, 

 under gradually increasing e.m.f., is given in the following 

 table, the reaction under a particular type being indicated 

 by an inclined cross. 



It is clear therefore that we have in all these cases a 



