38 E. J. LUND 



pressed by saying that a reaction by digestion is substituted for 

 one by extrusion. 'These facts appear in a clearer way when the 

 course of extrusion is studied in single individuals. 



A further analysis of these responses must be kept for a future 

 time, since the data from other experiments in which were used 

 other substances are not sufficiently complete. 



SUMMARY 



1. A quantitative method (p. 3) was worked out, by means of 

 which it was possible to study the processes in the food vacuole 

 of Bursaria. 



2. Yolk and vitellin may be drawn upon as food for the energy 

 requirements and growth of Bursaria. 



3. The liquid of the newly formed food vacuole is partly made 

 up of the external medium, and partly of an acid secreted by the 

 base of the buccal pouch. After a few minutes this liquid is 

 resorbed and the vacuole membrane becomes applied to the 

 yolk grain. The vacuole contents remain acid in reaction 

 throughout the process of digestion of vitellin and yolk grains. 



4. Sooner or later after the initial resorption of liquid about 

 the grain, digestion begins. Digestion may or may not result in 

 the second appearance of liquid in the vacuole, according to the 

 principle that whenever the rate of solution — this perhaps in 

 part depending upon the concentration of the cleavage agent — 

 is greater than the rate of resorption, then the liquid products 

 of digestion accumulate more or less about the grain, while if 

 the rate of solution of the grain is slower than the rate" of resorp- 

 tion, then the products of digestion are removed as fast as they 

 are formed. Equilibrium between these processes in the vacuole 

 may be established during digestion of vitellin with much, little, 

 or no hquid present in the vacuole. 



5. The average time for complete digestion of vitellen in Bur- 

 saria was found to be directly proportional to the square root of 

 the quantity of vitellin eaten, i.e., the relation expressed by 

 Arrhenius' formula t=kV m was found to hold to within the 

 limits of experimental error. 



