RELATIONS OF BURSARIA TO FOOD 29 



(fig. 1, Experiment I, from 144 to 288 hours, represents individuals 

 of this kind and constitutes evidence that the length of life of 

 individuals fed fresh yolk is greater than that of those fed fat 

 free yolk. During this time the quantity of fat in the cell de- 

 creases as starvation continues, indicating that the fat is used up. 

 Under some conditions no traces of fat can be found in Bursaria 

 by the use of Sudan III, but this of course does not prove its 

 complete absence. The apparent absence of fat is rare and it 

 was found difficult by means of starvation to remove the last 

 traces. 



3. Is fat formed from vitellin or starch in Bursaria? 



When yolk is extracted repeatedly with cold ether or with 

 cold alcohol, at intervals, for twenty-four hours or more, a white 

 residue remains, which is chiefly vitellin. Such vitellin was 

 fed to Bursariae which had been starved. An abundant fat 

 deposit appeared in the cytoplasm, indicating that yolk extracted 

 with cold ether or alcohol alone still contained a fraction 

 which appeared as fat in the cells. This was tested by extract- 

 ing fresh hard boiled yolk with ether-alcohol mixture for ten to 

 twelve hours in a Soxhlet apparatus. Vitellin so extracted was 

 fed to one of each pair of sister cells while the other cell was kept 

 as control. No difference appeared in the amount of fat present 

 in the two cells, although many attempts to demonstrate a differ- 

 ence were made. 



In view of the fact that crucial control tests were not made by 

 Nirenstein ('10) the slight difference in fat content given in his 

 figures 7 and 1, plate 1, cannot I think, be considered proof that 

 the fat found to be present in Paramecium (fig. 7) after digestion 

 of egg albumen, had been derived from the latter; furthermore, 

 analyses of egg albumen show traces of the presence of lipoids, 

 such as fat, cholesterin and lecithin. 



Various kinds of starch and paramylum grains which were 

 retained by Bursaria, remained intact for days and showed no 

 signs of corrosion or solution. 



