EELATIONS OF BURSARIA TO FOOD 23 



and since vitellin grains readily adsorb it in considerable quantity, 

 depending upon the length of time during which the grains are 

 left in the aqueous solution of the dye. 



The results of the experiment clearly show: (a) that the ad- 

 sorbed Congo red very markedly interferes with or prevents di- 

 gestion of the parts of the vitellin grain to* which the congo red 

 has been adsorbed, and (b) that it brings about a condition which 

 leads sooner or later to an extrusion of the contents of the vacuole; 

 (c) that it may exert a greater or less toxic effect from within 

 the vacuole, upon the cell, which may lead to an earlier death 

 than if the unstained vitellin had been eaten. In short: the chem- 

 ical nature of the substance taken into the vacuole of Bursaria may 

 determine in various ways what many of the conditions and reactions 

 of these organisms will he, and especially, in this connection, 

 the action of the digestive agent and the process of extrusion. ^ 

 The following are the results in brief. 



Experiment VI. Grains of vitellin of uniform size, prepared as de- 

 scribed above, were stained twenty minutes in a deep red aqueous solu- 

 tion of Congo red. They were then washed several times until no more 

 stain could be washed out. An unstained portion of the same vHellin 

 sample was washed the same number of times in tap water; this was 

 fed to the control individuals. Forty normal individuals previously 

 starved in tap water for 24 hours were each fed one grain of the stained 

 vitellin. Similarly a control set of 40 individuals were fed, each one 

 grain of the unstained viteUin. All the conditions and material were 

 the same in the two sets, except that the individuals of one set was 

 fed stained grains, those of the other set unstained ones. Both sets of 

 individuals were kept in watch glasses, each containing 4 cc. of spring 

 water. Two individuals were placed in each watch glass. Records 

 of each individual were taken 2, 4, 6, 7, 9, 11, 13 and 22 hours after 

 feeding. 



Table 6 gives the results. Table 6 (a) shows that the partially 

 digested or undigested congo red stained grains were to a large 

 extent extruded, while in the control set, all retained the unstained 



^ I. have here used the term 'chemical nature,' and in my previous paper (Lund 

 '14) such terms as 'toxicity' (p. 29), 'specific chemical properties' (p. 41), with a 

 general meaning. The finer distinction between the effects due to chemical and 

 physical properties of a substance, as for example its solubility in the plasma 

 membranes, state of colloidal aggregation, chemical reaction with the protoplasm, 

 etc., remains an open question. 



