22 E. J. LUND 



really conforms to the law of a heterogeneous chemical reaction 

 (between a solid and a liquid).^ 



The values in column 5, table 5, were obtained by substitution 

 in Arrhenius' formula t = kV M for the rate of digestion in the dog 

 as found by London. ^ The values obtained by means of this 

 formula agree well, within the limits of experimental error, with 

 those found by experiment in the case of Bursaria. 



In column 6, table 5, are given the values of k in the formula 

 t=kVM. The agreement is not so good in Experiment III as 

 in Experiment IV for reasons given above, although the variation 

 in the constant k of both experiments, and especially that of 

 Experiment IV, is well within the limits of experimental error. 



If it were possible, it would be interesting to determine what 

 the value of k would be for other food substances. 



The experiments show that in spite of individual variations 

 among the organisms and the variation in the process in different 

 vacuoles in the same individual which were mentioned above, 

 the sum total gives a definite result, and shows that the average 

 rate of digestion of vitellin under rigid experimental conditions 

 follows a definite law. 



4. Effect of Congo red upon the average velocity of digestion, 



extrusion, etc. 



In order to discover some of the changes which take place in 

 the reactions of the cell when protein (vitellin grains) was changed 

 by letting it adsorb a substance from solution, the following 

 experiment was carried out. Congo red was chosen since its 

 toxicity to Bursaria is low when compared to that of many dyes, 



1 The intermediate position of the values found suggests agreement with the 

 results of the experiments of Bajdiss ('04), who found that "with concentrations 

 of casein up to about 4 per cent, the velocity of digestion is proportional to the 



concentration of the substrate whilst with more than 8 per cent, 



inverse proportionality sets in" (cited from Euler: General chemistry of the 

 Enzymes, p. 186). Furthermore the results also suggest the possibility that the 

 quantity of active agent produced in the cell or vacuole is not directly propor- 

 tional to the quantity of vitellin eaten. 



2 This is, t = kVM-j where t is the time for complete digestion, il/ the amount 

 by weight eaten, and k a constant depending upon the nature of the food. 



