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PHOTIC SENSITIVITY OF CIONA INTESTINALIS 



IV. Effect of Intensity. 



1. In order to study the effect of different intensities of light on 

 the duration of the sensitization period, a single source of light was 

 used. This was a Mazda lamp of 120 candle power. By keeping 

 it at different fixed distances from the animal, six intensities were 

 secured, as given in Table II. 



Ten animals varying in size from 3.5 to 10.5 cm. were used for this 

 experiment. It may be said at once that no difference in sensitivity 

 was found for individuals of different size. The reaction time of 

 each animal to each of the six intensities of light was determined 

 three times; thus, eighteen observations were made on each animal. 



TABLE II. 



The determinations were purposely scattered over a period of 12 

 hours so that any fatigue effects would be avoided. In Table II, 

 Column 2, are given the average values for the reaction times of 

 the ten animals. Each figure represents an average of 30 determi- 

 nations. In addition the data are plotted in Curve A of Fig. 1. From 

 both these sources it is apparent that the reaction time varies in- 

 versely as the intensity. In Column 3 are given the values for the 

 sensitization periods corresponding to the different reaction times. 

 These were calculated by subtracting the duration of the latent 

 period, 1.76 seconds, from the reaction time values. 



2. On the supposition that the sensitivity of Ciona depends upon a 

 photochemical reaction, the relation between the intensity of the 



