Physiology 469 



of T. evansi (379) and T. hippicum (194) is essentially similar to that of 

 T. equiperdum. It has been suggested that T. hippicum, which lacks cyto- 

 chrome oxidase, is dependent upon the host for removal of waste pyru- 

 vate. However, it might be interesting to test T. hippicum and T. eqiii- 

 perdutn under conditions which would insure an adequate supply of 

 thiamine and other growth-factors in vitro. Such species as T. lexvisi (475, 

 517, 518) and T. rhodesiense (135) produce several intermediates. Succinic 

 forms about 40 per cent of the acids recovered from T. rhodesiense sus- 

 pensions in glucose-Ringer's solution, and is also a major product for T. 

 lexvisi. Both species also produce acetic, lactic, pyruvic, and formic acids, 

 ethanol and COo, and T. rhodesiense produces glycerol in addition. 

 Formate and COo appear only under aerobic conditions in T. lexvisi 

 suspensions. Whether succinate is produced through the tricarboxylic acid 

 cycle is uncertain. Since succinic dehydrogenase is cytochrome-linked and 

 T. rhodesiense presumably lacks the cytochrome system (32), this trypano- 

 some may be unable to oxidize succinate after producing it. This may not 

 be true for T. lexvisi which is rather sensitive to cyanide poisoning and 

 presumably contains the cytochrome system. 



Certain flagellates of termites decompose glucose anaerobically to car- 

 bon dioxide, hydrogen, acetic acid, and certain unidentified products. 

 Lactic and pyruvic acids, acetaldehyde, methyl glyoxal, and ethanol have 

 not been detected in significant amounts (217). 



In Plasmodium gallinaceum, hexokinase has been demonstrated (533), 

 and glucose, lactate, and pyruvate all seem to be oxidized through the 

 tricarboxylic acid cycle (535). The oxidation of pyruvate is inhibited by 

 malonate, with accumulation of succinate. Parasitized erythrocytes oxidize 

 pyruvate almost completely to CO2 and H^O by way of the Krebs cycle 

 and accumulate very little acetate. Cell-free suspensions of P. gallinaceum 

 produce considerable acetate, as well as CO^ and H2O, under aerobic con- 

 ditions and the acetate is not further decomposed; anaerobically, pyruvate 

 does not disappear and acetate is not formed (535). In P. knoxvlesi, lactate 

 is produced from glucose and can be oxidized (371, 570), and the increase 

 in lactate is more or less parallel to the production of pyruvate (571). 



Little is known about sugar metabolism of ciliates. Paramecium cauda- 

 tiun decomposes glucose to unidentified organic acids which account for 

 about a third of the sugar utilized (77). Tetrahymetia pyriformis produces 

 lactic, acetic, and succinic acids from glucose under anaerobic conditions 

 (550). When T. pyriformis was supplied with glucose and radioactive CO2, 

 all the radioactive carbon appeared in the carboxyl groups of succinic acid, 

 indicating that COo is assimilated in the production of succinate (550, 

 412), as previously reported for Trypanosoma lewisi under anaerobic con- 

 ditions (518). The oxidation of substrates through the tricarboxylic acid 

 cycle in ciliates is indicated by the presence of succinic dehydrogenase in 

 Tetrahymena pyriformis (311) and Paramecium caudaturn (215), and by 



