RELATIONS OF BURSARIA TO FOOD 37 



ent, towards the end of the experiment, in the individuals of 

 Sets B and C, was caused by rapid and complete digestion, then 

 the effect of mass on the rate of digestion for fresh yolk would 

 have to be relatively vastly more pronounced with fresh yolk 

 grains than is true for vitellin; and this is not the case. 



The first parts of the curves (fig. 8) bring out the points clearly, 

 for here the error, that would be caused by the loss of grains due 

 to complete digestion and not to extrusion, is practically avoided, 

 since the rapid fall in the number of grains takes place during 

 the first part of the experiment, before the digestive process could 

 have been effective in causing total disappearance of the yolk 

 grains; especially is this true for Set C, Curve C. On the other 

 hand. Curve A which we should expect to be markedly affected 

 by digestion, does in fact show only a slight fall, compared to that 

 of Curves B and C. It will be noted that the amounts of fall of 

 the curves show the same sequence as the number of grains fed. 



The, results therefore actually demonstrate beyond question, 

 that the quantity of fresh yolk eaten is a determining Jactor in 

 the process of extrusion. The greater the mass or volume the 

 more effective is the stimulus from the contents in the vacuole. 

 A quantitative or intensity factor as well as a qualitative factor 

 therefore enters and determines whether or not extrusion of fresh 

 yolk shall take place. 



Now from the results of Experiment VIII we have as yet no 

 evidence showing in what way the mass or volume affects the 

 process; i.e., whether it is an intensity effect due to chemical 

 or mechanical stimulus or both. 



Another important fact in connection with the extrusion re- 

 action is that the stimulus from the contents of the vacuole is 

 most effective in bringing about extrusion during a rather limited 

 period (4 to 6 hours with fresh yolk grains) after the formation 

 of the vacuole. This will be seen from the sudden drop in the 

 curves in figure 8, with subsequent tendency to retention of the 

 remains of the yolk. There is a process of functional adjust- 

 ment (loss of irritability?) with the continued action of the stimu- 

 lus from the contents of the vacuole. Roughly it may be ex- 



