2 E. J. LUND 



danger that the conditions may become so artificial as not to war- 

 rant conclusions concerning what occurs under usual ('normal') 

 conditions of the organism. Nevertheless, a certain degree of 

 simplicity may often be obtained in the conditions of experimenta- 

 tion and yet coincide with the usual conditions of a varied en- 

 vironment to a sufficient degree so that the results give a definite 

 answer to questions which are directed toward finding out what 

 the principles are which underlie the processes. The following 

 experiments have been carried out with an attempt to fulfill 

 the above requirements. 



In a previous paper (Lund '14) some of the most important 

 external relations of Bursaria to food have been presented, in- 

 cluding a demonstration of a selective extrusion among the food 

 vacuoles. 



The following paper deals with the processes which take place 

 in the food vacuole, and with the conditions under which it 

 exists as an active system in this unicellular animal. . 



Proteins, fats, and carbohydrates in the form of starches are 

 present in the material eaten by Bursaria, as may easily be de- 

 tected by direct observation or by the aid of microchemical 

 tests. Protein in the form of other living ciliates, flagellates, 

 etc., is taken in and digested. Many of these Protozoa which 

 serve as food contain fat globules and starch or amylum grains, 

 and hence all three food substances may at times be found present 

 in the cytoplasm of Bursaria from flourishing cultures. 



Since there is disagreement between results of different investi- 

 gators, working with the same Infusoria; but more particularly 

 because there are indications that similar forms among these 

 animals differ in their food metabolism, the statements here 

 made refer only to Bursaria and may or may not be valid for 

 others, except where specifically stated. 



