32 



E. J. LUND 



course if yolk which has been very strongly stained and not 

 washed out sufficiently, is fed, then the concentration of the 

 medium rises so quickly that they are greatly injured or killed. 

 Now against the conclusions which will be drawn from the re- 

 sults of Experiment XII (a) and (Id), as it stands, may still be 

 urged the objection that the reason that so few or no grains are 

 eaten, is because of what one might call a general injury or stimu- 

 lation of the celLby the saffranin which is rapidly being liberated 

 into the water, and that it may not have anything to do with a 

 specific reaction to the chemical character of the food particle as 

 such, that is, to anything hke a "sense of taste." That this 

 objection does not appl}^ to conditions like those in the above 

 experiment (XII, a and b) where the amount of stain adsorbed 

 even in dishes A and B is ver}^ little compared to that in Experi- 

 ment XIII, may be shown by taking the solution of dish .4, 

 Experiment XII (a), and placing unstained yolk and Bursariae 

 in it. The result of such an experiment is that the organisms 

 fill up with fresh yolk, showing that the medium in weaker con- 

 centrations does not affect the eating process to any appreciable 

 extent. Further proof of this will be given in the experiments 

 immediately following, and also in experiments to be given later. 



Experiment XIV. To test whether or not Bursaria can select and 

 eat non-toxic yolk grains from among toxic ones, when the two are 

 mixed. Two suspensions were made, one of yolk stained in saffranin 

 twenty-four hours, then washed out repeatedly, the other containing 

 the same kind of yolk washed in the same way but not stained. The 

 two yolk suspensions were mixed immediately l^efore the animals were 

 placed in the mixture. Twenty individuals were used. The time of 

 feeding was fifteen minutes; a control of washed unstained yolk alone, 

 was kept at the same time (table 15). 



TABLE 15 

 Experiment XIV 



MIXTURE 



Stained | 



Unstained 



Control : 

 Unstained yolk 12 



NUMBER OP GRAINS EATEN BY EACH INDIVIDUAL 



Oi Oj 

 2 3 2 



715 



Oj 

 2 4 2 



915 8 9 







2i 3: 2 



3I25I 7 



XIX 



x!x 



15il2 



XX 

 XX 



9 9 



X|X 



x'x 



si 8 







29 



213 



