34 



E. J. LUND 



suit. What is meant in this case by concentration gradient, is 

 the molecular concentration plus the specificity of the substance, 

 that is, in anthropomorphic terms we should say 'Hhe kind of 

 taste" which the substance has. That the specific nature of 

 the substance is one factor in determining the result, is shown 

 by a comparison of the results of numerous experiments with 

 safifranin, janus green, hematoxylin, and especially other less 

 toxic stains, like congo red (cf. what follows). 



b. Janus green. A considerable number of experiments have 

 been carried out using this substance, with the same general 

 results as those obtained with saffranin. It is better adapted 

 to bring out the phenomenon of selection than saffranin, causing 

 a sharp discrimination by Bursaria; small quantities adsorbed 

 bj^ the grains are sufficient to bring about rejection. The fol- 

 lowing experiments show some of the relations. 



Experiment XVI (a) and (6) . Yolk was stained in janus green twenty- 

 four hours then soaked in tap water and washed repeatedly. A portion 

 of the same kind of yolk soaked and washed in the same way but not 

 stained, was used as a control and for mixing with the stained yolk. 

 A few minutes before the experiment equal quantities of the stained 

 and unstained yolk suspension were mixed in dish A. A second quan- 

 tity of the unstained yolk suspension of a concentration equal to the 

 sum of those in dish A was placed in dish B. Twenty individuals were 

 placed in each dish and left to feed twenty minutes (table 18 a). 



TABLE 18 (a) 

 Experiment XVI (a) 



MIXTURE, DISH A 



NUMBER OF GRAINS EATEN BY EACH INDIVIDUAL 



Stained... 

 Unstained 

 Control, 



Dish B : 

 Unstained 



912 



21 



82012 



15 







4 5 



19 



1317 



1413 



15 



12 



OX 

 IX 



1917 



14 



XX 

 XX 



268 



The yolk in both dishes was now washed twice and the experi- 

 ment repeated with control. Time of feeding fifteen minutes. 

 The count is shown in table 18 b. 



In (a) the solution had become sufficiently strong to affect 

 five of the animals (X), so that thej? could not be recovered for 



