RELATION OF BURSARIA TO FOOD 51 



food is completely digested, because the maxima of the curves 

 A and B of //, and of B, I, occur at the same time. We there- 

 fore have a demonstration of the selective extrusion among vac- 

 uoles as well as of a process of selection in feeding in Bursaria. 

 Similar curves may be worked out for Sudan III or powdered 

 aliuninium. 



SUMMARY 



1. Bursaria has three ways of rejecting solid particles, as shown 

 by the paths over which the particles are passed. These are: 

 (a) the path of total rejection, shown by particles which never 

 enter the oral apparatus; (b) the path of rejection of large par- 

 ticles, this being a retracing in the opposite direction of the 

 path by which they entered; (c) the path of rejection of small 

 particles, which leave the oral pouch by way of the base of the 

 oral sinus and are passed backward over the ventral side of the 

 bod}^ (fig. 1). 



2. No definite path is followed by the food vacuoles during 

 digestion, and in their passage through the cytoplasm. Residues 

 are eliminated from a small area on the mid-dorsal side of the 

 cell. 



3. Grains of fresh hard boiled yolk of hens egg, when prepared 

 as described (page 8), furnishes a good unit of measui'e of the 

 food taken, and an easy means for determining the factors which 

 come into play in the process of feeding in Bursaria. 



4. The amount of food eaten and the rate at which it is eaten 

 depends upon the physiological state of the cell (defined on page 

 10). This is shown to be true for fresh and for fat-free yolk, 

 and also for indigestible substances such as aluminium, Sudan 

 III, Chinese ink, etc. 



5. Change in the physiological state of the cell is indicated 

 by the change in the total amount eaten and the rate of feed- 

 ing, under the same conditions. 



6. The rate of feeding is not affected in proportion to the 

 concentration of the yolk suspension. 



7. Mechanical stimulation decreases the rate of feeding or 

 inhibits it, roughly in proportion to the degree of stimulation. 



