AEROBIC FERMENTATIONS 165 



ed to supply a storage material which can subsequently 

 be utilized in times of need by means of aerobic oxida- 

 tions; though the fat synthesis releases some energy, 

 that energy production is of secondary importance to the 

 animal. On the contrary, in the aerobic or anaerobic 

 fermentations which occur in Fasciola, Moniezia or Gas- 

 teropJiilus and which have higher fatty acids as end 

 products, energy production is the essential feature and 

 the same higher fatty acids that, in the other cases, rep- 

 resent su?h important storage products are here generally 

 only waste products. The ability to form reserve fat 

 from carbohydrates is probably widespread amongst 

 invertebrates. There is good evidence that the process 

 occurs in protozoa (Nirenstein, 1910; Doflein, 1918; 

 Pringsheim, 1928; Zingher, 1933), in snails (Biedermann, 

 1911) and in insects (Melampy and Willis, 1939; Wig- 

 glesworth, 1912). It seems likely that many more cases 

 will be discovered. Now, Zhinkin (1930) and Barbarine 

 (1938) reported that various free-living protozoa trans- 

 form glycogen into fat when oxygen is lacking and that 

 this fat, in turn, disappears, i.e., is used for energy pro- 

 duction when the medium again receives a sufficient sup- 

 ply of oxygen. Thus, under one set of conditions, the 

 fat is a metabolic end product which is not utilized fur- 

 ther as long as these conditions prevail, and which is 

 directly comparable to the fat excreted by Moniezia or 

 Fasciola, where it seems never to be used for the pro- 

 duction of energy. Under another set of conditions 

 (good ox3'genation) this same fat represents for the 

 protozoa an energy reserve and has exactly the same 

 importance as fat synthesized from carbohydrate and 

 deposited in the tissues of aerobic animals as a reserve 

 against future needs. 



B. Relations of aerobic fermentations ivith other meta- 

 bolic processes. In this section only those incomplete ox- 

 idations will be considered in which energy production 



