26 E. J. LUND 



It is not to be supposed that the appearance of Hquid in food 

 vacuoles generally, under other conditions, need necessarily be 

 due to rapid digestion and slow resorption (cf. fig. 3). In such 

 cases we may have other factors bringing about accumulation of 

 liquid. 



Other tests of the effect of congo red upon digestion gave simi- 

 lar results, but since records of individuals were not taken these 

 results are not expressible quantitatively. 



DIGESTION AND RESORPTION OF FAT 



1. A demonstration of fat digestion and resorption in the food vacuole 



of Bursaria 



Nirenstein ('10) and Issel have furnished a simple and reliable 

 method for determining the presence of lipoids in infusoria.^ 

 The method consists simply in placing a small drop of the culture 

 fluid containing the Infusoria on a slide and killing and staining 

 by addition of a few drops of an alcoholic solution of Sudan III. 

 The mount is cleared with NH4OH followed by thick glycerine. 

 By proper manipulation beautiful mounts may be obtained. 

 The gross distribution of lipoid in the cell is faithfully preserved 

 by this method. This is shown by the fact that fat globules of 

 the same typical sizes as in the mounts may readily be distin- 

 guished in the ground substance of the living protoplasm and 

 followed during protoplasmic movement especially in individuals 

 with high fat content. Bursariae taken directly from healthy 

 cultures always had more or less fat present in the protoplasm. 

 This fat is probably derived from other Protozoa which serve as 

 food. 



When an individual from a wild culture, with a high fat con- 

 tent, is isolated and placed in tap water, the protoplasm usually 

 becomes clearer after one or more days; showing that fat, as fat 

 droplets at least, disappears from the cell. 



The chief reason for the difference in results and conclusions 

 of Nirenstein ('10) and Staniewicz ('10), as to whether Infusoria, 



^ The words 'lipoid' and 'fat' are used here to designate mainly those fat-like 

 Substances in the cell which are amenable to detection by microchemical tests. 



