152 CYTOPLASMIC INCLUSIONS 



termediate granules being visible. These cytoplasmic fat droplets are not 

 derived directly from fat in the food vacuoles, but the ingested fat is 

 absorbed as free fatty acid and glycerine, synthesized into neutral fat in 

 the cytoplasm and then stored as granules (Mast, 1938) . Free fatty acids 

 were demonstrated in the food vacuoles when fat was being digested, 

 but none were demonstrated in the cytoplasmic fat droplets or on their 

 surface when they were being formed. In the cases in which this process 

 is not visible, either the synthesis is carried on elsewhere and the fat trans- 

 ported to the granules as such, or the fatty acids are never allowed to 

 accumulate sufficiently to show under the microscope. 



The visible lipoids, i.e., those which are found in definite globules 

 and demonstrable by the ordinary fat-staining technique, include only 

 a part of the total lipoids of the cell. "The pathologists have known for 

 many years that the fats and fat-like substances of protoplasm are so 

 bound or united to proteins as to be for the most part non-recognizable 

 in the living or stained cell" (Heilbrunn, 1936). Besides the factors of 

 food and the formation of fat from other substances such as carbohy- 

 drate or protein, changes from bound lipoids to free globules must be 

 considered in any estimation of the reserve lipoids. Heilbrunn demon- 

 strated an increase in lipoid globules in specimens of A. proteus kept in 

 a dilute solution of ammonium «salts. Three types of amoebae were found 

 — those which show lipoids in culture, those in which lipoid globules 

 appear after treatment with NH^Cl, and those in which no free lipoid 

 appears even after treatment. In similar experiments with Arbacia eggs, 

 Heilbrunn showed that the total lipoids of the protoplasm remained con- 

 stant; therefore the newly visible bodies are derived from bound lipoids, 

 not from new fat formation. Since ammonium salts in the culture medium 

 raise the pW of the immersed cells, the results were attributed to alka- 

 linization of the protoplasm. The fact that COo bubbled in the medium 

 (which would tend to lower the protoplasmic /'H), inhibits the forma- 

 tion of visible lipoids, confirms this hypothesis. Old cultures of Para- 

 7necium show larger amounts of fat than new cultures, although the 

 paramecia divide and show no ill effects (Zinger, 1933) ; and since such 

 cultures contain ammonia (Weatherby, 1927), the presence of abnormal 

 amounts of visible fats may be due to the resulting alkalinization of 

 the protoplasm. 



Ultra-violet radiation causes a release of lipoid in Amoeba (Heil- 



