RELATION OF BURSARIA TO FOOD 11 



a definite and strict separation of the internal and external of 

 any living organism, and especially is this true of the cell. Yet 

 for purposes of presentation, this becomes highly convenient, 

 and it is only for this purpose that the above rough distinction 

 is made here. When all external conditions are made the same in 

 two experiments which nevertheless give different results, the differ- 

 ences must he attributed to different coiiditions within the organism, 

 and it is, as a rule, only in this way that different physiological 

 states are at present practically perceptible. 



Differences in physiological state in unicellular animals are 

 made evident most readily in the relations to food, as may be 

 seen from the work of Metalnikow ('12) on Paramecium and by 

 Schaeffer ('10) on Stentor. 



Bursaria affords most excellent material for the elucidation of 

 the relation of these dynamic states to the feeding process and 

 of the fact that this relation changes while the external con- 

 ditions remain constant. These facts are brought out in the 

 following experiments by using both single individuals, and large 

 number^ of individuals collectively, at the same time, and analyz- 

 ing the results. 



The total quantity eaten and the rate of feeding. Table 1 

 gives the results of a typical experiment designed to show the 

 difference in the total quantity of food eaten and also the differ- 

 ence in the rate of feeding of Bm'saria from different cultures. 



Material from two different cultures, A and B, was starved 

 twenty-four hours in each of two dishes containing 400 cc. of 

 tap water. 1 cc. of a fresh hard boiled yolk suspension was placed 

 in each of 16 stender dishes of 8 cc. capacity; 5 cc. of tap water 

 was then added to each. Thirty individuals from culture A 

 were placed in each of 8 of the dishes. Alternately with these 

 8 sets from culture A were placed 8 sets of thirty individuals each 

 from culture B in the other 8 dishes. At the end of the time 

 intervals noted in the table, in each case, the contents (6.5 cc.) 

 of one dish each of A and of B were transferred into a stender 

 dish with 500 cc. of tap water. This stops the feeding. The 

 individuals were then immediately picked out of these large 

 dishes, placed in 8 cc. dishes and killed in Meves' fluid. The 



