RELATION OF BURSARIA TO FOOD 



33 



In the mixture the concentration of the saffranin rose so rapidly 

 that some of the individuals were killed,^" This is indicated 

 above by X. Yet even in such a strong solution, selection took 

 place, though the number of grains eaten was small compared 

 to the number in the control. 



Experiment XV. Another sample of 3'olk less deeply stained than 

 that in Experiment XIV, was washed out many times and mixed with 

 an equal quantity of unstained yolk from the same sample. Thirty 

 individuals of the same material as used in Experiment XIV, were 

 fed for five minutes, instead of fifteen minutes as before (table 16). 



TABLE 16 

 Experiment XV 



A repetition of the above experiment with yolk stained a little 

 more deeply gave the following result; twenty individuals used; 

 fed five minutes (table 17). 



The control of Experiment XIV will likewise serve for Experi- 

 ment XV. 



The results of this experiment are to be explained by the fact 

 that the concentration gradient of the adsorbed toxic saffranin 

 is relatively low with respect to the gradient of the water-soluble 

 yolk substance to which Bursaria reacts in a strongly positive 

 manner. Of course one is not to suppose that it is the relati\'e 

 molecular concentration gradient alone that determines the re- 



^° The cytolytic action of saffranin is in some ways more marked than that of 

 janus green. The character of its reversible adsorption reaction also makes it 

 less suited for use in experiments of this kind than janus green, as will appear 

 from results with the latter. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 1 



