30 



E. J. LUND 



easily than if it could be washed out quickly, and one is also 

 able to control the concentration gradient between pure water 

 and the dye adsorbed by the yolk grain. The toxicity of the 

 different dyes varies greatly, and it was found that saffranin 

 and janus green were best from this point of view also, since 

 both of these are very toxic to Bursaria in higher concentrations 

 but only slightly so in lower concentrations. 



1. Experiments with stained and unstained yolk 

 a. Saffranin. 



Experiment XII (a). Object, to test (a) whether or not Bursaria 

 will eat yolk grains which have adsorbed an appreciable amount of the 

 soluble toxic substance saffranin and (b) whether or not the amount 

 of yolk eaten depends, in this experiment, upon the amount of saffranin 

 adsorbed. 



Equal volumes of a strong suspension of fresh yolk were placed in 

 each of seven stender dishes of 8 cc. capacity. A bright rose-colored 

 solution of saffranin was made up with tap water. To the dishes 

 designated A, B, C, D, E and F was added 5, 4, 3, 2, 1, and 0.5 cc. re- 

 spectively, of this solution, and mixed thoroughly. The seventh dish 

 without stain, was kept as a control. The suspensions were left to 

 settle five minutes, then decanted and 5 cc. tap water added to all the 

 dishes; this was repeated three times. The organisms used were starved 

 twenty-four hours and were in excellent condition. The time of feed- 

 ing was fifteen minutes (table 13) 



TABLE 13 

 Experiments XII (a) 



SAFFRANIN 

 SOL. 



NUMBER OF GRAINS EATEN BY EACH INDIVIDUAL 



A.... 



B.... 

 C... 

 D... 



E.... 

 F.... 

 Control! 

 G I 



0; 



Oi 3 

 8 

 2 

 2 1 

 4^0 



912 



0(3 



01 7 



5 

 34 

 61 

 56 

 113 

 138 



188 



When stronger solutions of saffranin than that in A were used, 

 no grains were eaten. All the animals at the end of the experi- 

 ment were normal and had not been injured. The yolk of dish 



