SUMMARY 253 



been reported in protozoa, in free-living and parasitic 

 worms and in arthropods, but rarely in molluscs, and 

 never yet in ecliinoderms ; they might occur in coelenter- 

 ates. 



2. The best evidence for aerobic fermentations is the 

 direct demonstration that non-oxidized or partly oxi- 

 dized substances are formed when oxygen is plentiful. 

 The resj)iratory quotient and the rate of carbohydrate 

 consumption are not infallible criteria. 



3. The assumption that oxidations remain incomplete 

 in the presence of a surplus of oxygen (aerobic fermenta- 

 tions) because the organisms were previously adapted to 

 an anaerobic life and are now incapable of utilizing oxy- 

 gen does not hold in the case of blood parasites in which 

 the ability to utilize oxygen from the erythrocytes has 

 been demonstrated. 



4. Some aerobic fermenters can perhaps obtain energy 

 from both the syntliesis and the breaking down of fat, the 

 former in the absence of air, the latter in aerated media. 

 (This is in contrast with what generally happens in most 

 animals : usually in aerobic organisms the synthesis of 

 fat from carbohydrates serves to store energy for future 

 need, and liberation of energy during this synthesis is 

 only incidental ; in anaerobic organisms, on the contrary, 

 the fatty acids formed are waste end-products, and the 

 energy production during fat synthesis is the essential 

 feature.) 



5. The relative importance of aerobic fermentations 

 and of other metabolic processes in supplying energy has 

 been studied primarily in parasitic worms. It has been 

 claimed that aerobic fermentations alone furnish all the 

 energy required by the worms and that the energy gained 

 by aerobic oxidations is wasted. Recent investigations, 

 however, indicate that the two processes are interdepen- 

 dent and that the energy derived from both sources may 

 be used by the parasites in aerated surroundings. 



