REVERSION IN ORIENTATION TO LIGHT 517 



not due to evaporation of chloroform, for if, after this reversion 

 has occurred, fresh negati\'e specimens are added to the solution, 

 the}' become positive at once and then after a few minutes nega- 

 tive. That is, they respond just like the original colonies did 

 immediately after the chloroform was first added. 



The results obtained with chloroform and ether were quite 

 as definite and conclusive as were those obtained with acids, 

 but those obtained with chloral hydrate were much less definite. 



In reference to the acids, it was concluded that their action on 

 orientation, is probably associated with the time-rate of change 

 in the concentration of the hydroxy 1 ions in the culture solution. 

 The action of the chloral hydrate may have been due to the same 

 cause, for it was slightly acid in reaction, but the action of the 

 chloroform and ether could not have been due to this for both 

 gave distinct alkaline reactions with neutral red. Moreover, 

 it was found that chloroform produces reversion in negative col- 

 onies in chemically pure water, i.e., in a solution practically 

 de\oid of free hydroxyl ions. 



EFFECT OF TEMPERATURE AND ILLUMINATION 



The effect of illumination and temperature on the sense of ori- 

 entation was not intensively studied. But the observations 

 made indicate that strong light tends to induce negative, and weak 

 light positive orientation, and they demonstrate clearly that an 

 increase in temperature tends to make Spondylomorum positive 

 and a decrease tends to make it negative. The relation between 

 temperature or illumination and the sense of orientation is, 

 however, not specific. For example, under certain conditions, 

 colonies were found to be positive in all temperatures above 14° 

 and negative in all below about 10°, while under other conditions 

 the same colonies were found to be negative up to nearly 42° 

 and positive above this temperature. Similar results were re- 

 peatedly obtained. Moreover, under certain conditions, rever- 

 sion in orientation could not be induced by changing the tem- 

 perature, and under other conditions it was observed without 

 any change in temperature. Changes from positive to negative 

 orientation in constant temperature are particularly prevalent 



