CHAPTER II 



AEROBIC FERMENTATIONS 



Oxidations may be incomplete even in presence of an 

 abundant supply of oxygen. When this is the case, one 

 may find in one and the same animal some incomplete 

 oxidations that do not utilize any molecular oxygen and, 

 proceeding at the same time, but more or less inde- 

 pendently, the ordinary, complete aerobic oxidations. 

 In other organisms the metabolism may be only partially 

 aerobic, that is, molecular oxygen enters into the re- 

 actions but the oxidations remain incomplete. 



Some of these reactions are referred to in the lit- 

 erature as aerobic glycolysis or as aerobic fermentations. 

 This latter expression will be used throughout the pres- 

 ent review. 



Several criteria may be used to determine the presence 

 of aerobic fermentations. A respiratory quotient above 

 1 in well oxygenated surroundings proves that the oxi- 

 dations are incomplete — as, for example, in the case of 

 freshly isolated specimens of Ascaris for which von 

 Brand (1934a) reported an R.Q. of about 4 — but a 

 low R.Q. does not prove that they are complete. Thus, 

 in cases in which incomplete oxidations in presence of 

 abundant oxygen were observed by other criteria, the 

 respiratory quotient was either abnormally low, for 

 example, 0.16 in Trypanosoma rJiodesiense (Christophers 

 and Fulton, 1938) or it was in the neighborhood of 1, 

 for example, 0.95 in Leishmania tropica (Soule, 1925) 

 or exactly 1.0 as in Strigomonas fasciculata and Strigo- 

 monas oncopelti (Lwoff, 1934). 



A fairly reliable indication of aerobic fermentations 

 may be obtained by a comparison of the rates of carbo- 

 hydrate consumption under aerobic and under anaerobic 

 conditions. In purely aerobic animals the two rates us- 



