28 E. J. LUND 



cell (fig. B) had been fed olive oil. Figure B shows the sister 

 cell twenty-four hours after feeding with olive oil. The large 

 fat drop in B constituted the contents of the food vacuole previous 

 to mounting. Both cells were starved in tap water for eighteen 

 hours previous to feeding of sister cell (fig. B). The same results 

 were obtained when fresh yolk grains were fed. 



These experiments prove conclusively that in Bursaria the 

 fat in the food vacuoles passes out in one form or other through 

 the membrane of the food vacuole, and becomes distributed in 

 the cytoplasm as small droplets. This agrees perfectly with the 

 results obtained by Nirenstein ('10) for Paramecium. Liquid 

 may at times be present about the fat droplets undergoing 

 resorption in the vacuole, just as in the case of vitellin or yolk 

 (plate 1, H to L). But no attempt was made to study its changes. 

 Results from a study of the chem'ical changes involved in digestion 

 and resorption of fat will be given elsewhere. 



'2. Role of fat in growth and energy requirement 



The tail, in the form of Bursaria studied, serves in general, 

 as a convenient index of the degree of 'fatness' or 'leanness' of 

 this organism. 



When olive oil is fed to a large number of Bursariae under 

 favorable experimental conditions, so that more or less resorption 

 takes place, the fed animals, on the average, become larger than 

 the unfed. The tail on the average also assumes more pronounced 

 outlines than those of the control. In such large individuals 

 when in sufficient number for comparison with the controls, there 

 is indication also that the length of life is on the average in- 

 creased by having eaten olive oil. When individuals fed a defi- 

 nite number of grains (1 or 2) of fresh yolk, are compared with 

 others fed the same number of fat-free yolk grains, the individuals 

 fed with fresh yolk, become on the average larger, many of them 

 attaining a relatively enormous size. During this growth per- 

 fect proportions of form are maintained. Such large individuals 

 are always found to contain much fat. The part of the Curve A 



