RELATIONS OF BURSARIA TO FOOD 27 



particularly Paramecium, actually do digest, resorb, and utilize 

 fat for the energy requirements of the cell, appears to be the fact 

 that these investigators did not compare the fat contents of 

 the same cells nor sister cells, before and after feeding of fat, but 

 limited their comparison to different individuals taken at random 

 from the same culture. 



In order to leave absolutely no question as to the fact of di- 

 gestion and resorption of fat in Bursaria, cells which were in the 

 process of division were isolated from the wild cultures. Those 

 which had many vacuoles were discarded, and in most cases only 

 those with no food vacuoles were used. Each pair was placed in 

 a separate watch glass with tap water. After the completion 

 of division, or after eighteen to twenty-four hours' starvation in 

 the tap water, one of the sister cells was fed an emulsion of olein 

 or pure olive oil (both gave the same results), while the other 

 sister cell was kept as a control in a separate watch glass with 

 tap water, under exactly the same conditions. 



In different experiments, at different intervals after feeding, 

 both sister cells were tested simultaneously for the amount and 

 distribution of the fat content. In every experiment, after a 

 sufficient length of time, the cell which had eaten and retained 

 the olive oil or olein for some time showed an abundance of fat 

 droplets distributed throughout the cytoplasm, while the re- 

 maining fat in the vacuoles appeared as large, single fat droplets 

 or as groups of such. 



The fat content of food vacuoles can of course be readily seen 

 and followed in the living cells. In the control (sister) cell a 

 much smaller quantity of fat was invariably present, this quantity 

 depending upon the original amount present in the cell before 

 isolation. 



That the fat is distributed equally to sister cells in dividing 

 individuals which have no food vacuoles at the time of isolation, 

 was of course tested by mounting sister cells and comparing 

 the fat contents. 



The result of a typical experiment is given by the camera 

 lucida drawings. Plate 2, figure A, shows the control with a 

 small fat content twenty-four hours after the time when its sister 



