MOTOR RESPONSES 305 



in intensity. For example, if dark-adapted colonies are exposed to light 

 of 22,400 meter-candles for 0.05 minutes then returned to darkness, it 

 takes 20 minutes or more in darkness to eliminate the effect of the light. 

 This indicates that, under these conditions, the processes which occur in 

 light proceed at least 400 times as fast as the reverse processes which 

 occur in darkness. 



To account for the phenomena described, it is necessary to postulate at 

 least three interrelated processes, some of which must be directly corre- 

 lated with light in such a way that change in illumination of very short 

 duration can cause complete reversal in the nature of the response. It is 

 altogether probable ( 1 ) that some of these processes are photochemical 

 reactions; (2) that others are dependent upon the results of these; and 

 (3) that all are closely correlated with the physiological state of the 

 organism as^a whole (Mast, 1932b). The evidence now available clearly 

 indicates that such simple processes as those postulated by Mast (1907) 

 in his first publication dealing with this problem, and those postulated 

 by Luntz (1932) are very inadequate (Mast, 1932b). 



A considerable number of other facts have been established concerning 

 reversal in Volvox and related forms. For example, increase in tempera- 

 ture of hydrogen-ion concentration, and some anesthetics (especially 

 chloroform) cause photonegative colonies to become strongly photo- 

 positive. However, they usually remain positive only a few moments, 

 then become negative again (Mast, 1918, 1919). There is also a very 

 interesting correlation between reversal in light and response to elec- 

 tricity, in that photopositive colonies always swim toward the cathode 

 and photonegative colonies toward the anode (Mast, 1927c). These 

 facts show that reversal in light is not due to direct action of environ- 

 mental factors. They also indicate that it is correlated with the rate of 

 metabolism; but there is no clue to the nature of the processes involved. 



Responses to Electricity 

 a. rhizopods 



All the rhizopods which have been investigated {Amoeba, Pelomyxa, 

 Difjlugia, Arcella, Actinosphaenmn, and others) respond to electricity. 

 Kiihne (1864) and Engelmann (1869) observed that if they are sub- 

 jected to a series of induction shocks (alternating current), streaming 

 in them stops and they then round up. Verworn (1895), from observa- 



