44 E. J. LUND 



aluminium and those that do eat it generally take in only a 

 small quantity. This is also true of Sudan III and of carbon 

 black. The quantity eaten varies with the conditions in a 

 similar way, as previously set forth for yolk. Now if fresh yolk 

 grains are added to the suspension of aluminium the animals 

 will often quickly fill up with yolk, but in this case flakes of 

 aluminium become attached to the yolk particles and hence often 

 considerable quantities of the metallic aluminium are passed into 

 the body along with the yolk. Sometimes the quantity of yolk 

 eaten in such a mixed suspension is less than that in the control. 

 This serves to illustrate the sort of equilibrium which exists 

 between the organism and the kinds of substances in suspension, 

 partly determining the amount of food and other substances 

 eaten. 



2. The internal relations 



It was interesting to find that Bursaria possesses what I shall 

 call an internal compensating reaction to those substances which 

 are eaten to some extent, but are not digestible, such as Sudan 

 III, Chinese ink, powdered aluminium, and so forth. This com- 

 pensating reaction makes up to some extent, in the ''economy 

 of the organism" for the lack of a perfect discrimination between 

 indigestible ('tasteless') substances and those which can serve as 

 food. It is shown by the fact that indigestible substances are 

 eliminated from the cell usually a long time before the digestion 

 of a similar quantity of food is completed. This may be shown 

 with Sudan III. The results of the experiments are, for the 

 sake of brevity, given by curves. 



Experiment XXIV: Figure 4- Three sets of twenty-four individuals 

 each were fed Sudan III, cold-ether-extracted yolk, and fresh yolk 

 respectively. They were placed two in each watchglass containing tap 

 water in moist chambers, and examination in this case was made at 

 the end of three, seven, and twenty-two hours. Points on the abscissae 

 indicate the length of time in hours after feeding, while points on the 

 ordinates show the number of individuals which had extruded Sudan 

 III (curve .4) in the time intervals between the examinations, or in 

 the case of extracted yolk (curve B) and fresh yolk (curve C) the nu- 

 ber of individuals that had lost all traces of food. In this experiment 

 the observations were not sufficiently frequent to bring out the actual 



