262 VASIL OBRESHKOVE 



The Bunsen-Roscoe law can be expressed: 



(1) 7 X T = K, 



where I stands for the intensity of light, T indicates the reaction- 

 time, and K the constant effect produced. By transposing, this 

 equation can be written: 



(2) 7 = ^ or ^ 



where the constant effect, K, produced has been considered as 

 unity. In this form we have a reciprocal relation and for practi- 

 cal purposes it can be interpreted to mean that the constant 

 amount of work done divided by T, the time in which the work is 

 done, expresses the velocity of change or the rapidity with which 

 this is done. The greater T becomes, the slower becomes the 

 velocity of change, and this whole relation from the nature of 

 the equation is dependent upon the intensity of light. 



A graphic representation, therefore, of the data secured under 

 the conditions: 1) sensitivity of eye and skin and, 2) skin alone, 

 when the reciprocal of the reaction-time is plotted as function of 

 the intensity (equation 2) produces a curve which illustrates 

 the velocity of chemical change. This is shown in figure 6, 

 where for curve A the data in table 2 were employed; for curve 

 B the average reaction-times of blind tadpoles as shown in 

 table 4 were used in addition to the results obtained with 1.2 

 candle-meters as recorded in table 3. 



It is obvious from the two curves, that the velocity of change 

 in the receptors is approximately linear up to 15 candle-meters, 

 above which a gradual deviation occurs. This has already been 

 observed in the tables on intensity-reaction-time products in 

 three sets of readings, under three different conditions (tables 

 1, 2, 3). 



In reflex actions due to light, Hecht ('18) observed in Ciona 

 intestinalis a delay in the response after sensitization during 

 which the animal need not be illuminated in order to respond. 

 This secondary period he has termed the ' latent period, ' and for 

 Ciona he has assigned to it a value of 1.7 seconds. In subse- 

 quent researches Hecht ('19 a, b) has demonstrated the striking 



