Physiology 465 



of the common storage of cytoplasmic fats and oils, and the absence of 

 evidence that different enzyme systems are involved in storage and utiliza- 

 tion of lipids. Amoeba proteus apparently hydrolyzes several animal and 

 vegetable oils after their injection into the cytoplasm (89), and also di- 

 gests fats in food vacuoles (387). The products of digestion pass into the 

 cytoplasm and are combined there to form droplets of neutral fat (387). 

 Unlike amoebae, certain trypanosomes apparently do not produce lipases 

 (302). 



NITROGEN METABOLISM 



For certain phytoflagellates no amino acid need be supplied from 

 external sources. Therefore, the major feature of nitrogen metabolism 

 presumably is the assimilation of ammonium-N in synthesis of the amino 

 acids needed for growth. In Chilomonas Paramecium and Polytoma ocel- 

 latum, these syntheses apparently include all the amino acids which are 

 absolute requirements for Tetrahymena geJeii (182). Such flagellates may 

 have some promise in tracing the intermediate stages and the growth- 

 factors involved in synthesis of amino acids. Perhaps the general tech- 

 nique of "inhibition analysis" (525) will prove applicable here. 



The fact that certain phytoflagellates can grow on a single amino acid 

 indicates that transaminations may be as effective, in a general way, as 

 the assimilation of ammonium-nitrogen from an inorganic source. Utiliza- 

 tion of an amino acid as the sole source of energy has not been demon- 

 strated and the dissimilation of amino acids has not yet been traced. A 

 little more is known about the metabolism of amino acids in other Pro- 

 tozoa. Strains of Tetraliymena pyriformis seem to need eleven amino 

 acids, ten of which are considered irreplaceable for higher animals (10). 

 T. pyriformis undoubtedly synthesizes additional amino acids. In a 

 chemically defined medium stripped to essentials, these syntheses must 

 involve transaminations with at least certain number of the eleven serv- 

 ing as nitrogen-donors. However these reactions have not yet been 

 traced. 



The production of ammonia — reported for Bodo caudatus (310), Leish- 

 mauia tropica (498), Acanthamoeba casteUanii (46), Plasmodium gal- 

 linaceum (408), Didiyiiiim nasutum (567), "Glaucoma" pyriformis (100, 

 362), Paramecium caudatum (77), Spirostomum ambiguum (532) — in- 

 dicates that such species can deaminate amino acids but nothing is known 

 about the specific dehydrogenases involved. 



For Protozoa in pure cultures there is little critical information on 

 nitrogenous excretory products. The rather general production of am- 

 monia, and also the failure of tests for urea and mic acid in cultures of 

 Tetrahymena pyriformis (362) and in washed suspensions of Paramecium 

 caudatum fed powdered fibrin (77), have suggested ammonia as the 

 probable excretory product. 



