RELATION OF BURSARIA TO FOOD 39 



That the yolk grains are eaten, though to a less extent, even 

 after having been left in the solution of 50 drop concentration 

 for three and one-half hours, is shown by the following: Feeding 

 was limited to three minutes, which in part accounts for the 

 comparatively small number of grains eaten. Ten individuals 

 were used. The count gave 4, 2, 1, 6, 1, 1, 2, 0, 0, 1, a total of 

 18 grains of the deeply stained yolk. When this deeply stained 

 yolk in the 50 drop concentration of hematoxylin was washed 

 four times in tap water and tested again; the following count 

 was made: 11, 13, 14, 6, 5, 2, 12, 2, 4, 5, a total of 74 

 grains. 



These tests show (a) that although a dye may be toxic to 

 Bursaria, it may nevertheless not affect, to any great extent, the 

 functioning of the feeding mechanism in the taking in and swal- 

 lowing of the food, though (b) with some dyes total rejection 

 of the food may take place, when the concentration is so low 

 that it has only a comparatively slight cytolytic effect. The 

 former condition is shown to a less marked extent in the experi- 

 ments with saff ranin than in the experiments with hematoxylin ; 

 while the latter condition is illustrated by the results with janus 

 green. This seems then also to strongly suggest that different 

 substances may affect different parts of the cell differently. 

 Corroborative evidence upon this point, which it would be out 

 of place to consider here, has been obtained from observations 

 showing that the localization of the beginnings of cytolysis of 

 the cell body of Bursaria may differ with the particular nature 

 of the toxic agent employed. 



d. Congo red. Another stain which is adsorbed readily is eongo 

 red. This, however, unlike hematoxylin, can only be washed 

 out in part, that is, its adsorption reaction is not completely 

 reversible. Also since this dye is not as toxic as saffranin or 

 janus green, a large quantity of the stain may be adsorbed and 

 yet not appreciably affect the number of grains eaten, as is 

 shown by the following experiment. 



Experiment XXI. The yolk was stained twenty minutes in a strong 

 aqueous solution of the dye. Time of feeding twenty minutes. Thirty 

 were used (table 23). 



