SUMMARY 



The place of anaerobic processes in the general metab- 

 olism of invertebrates. 



1. A new classification of the chief energy-yielding 

 metabolic reactions occurring in invertebrates is proposed 

 which shows the relative importance of aerobic oxidations 

 and of aerobic and anaerobic fermentations. 



2. It is emphasized that truly anaerobic invertebrates 

 are found only amongst the protozoa, and that even these 

 may consume or perhaps require traces of oxygen for 

 their continuous well-being. 



Basis for the differences in anaerobic functions among 

 invertebrates. 



1. Of the various theories proposed to explain why 

 anaerobic protozoa and other animals that live habitu- 

 ally in environments with low oxygen content are in- 

 jured by oxygen, only one is supported by experimental 

 tests, the one which holds that the injury is due to the 

 toxic action of the hydrogen peroxide formed from the 

 oxygen present, the catalase content being insufficient to 

 destroy the peroxide. 



2. Some invertebrates withstand well the deprivation 

 of oxygen, others are rapidly paralyzed or killed. The 

 former are evidently able to gain sufficient energy for 

 their life processes through fermentations. (In many 

 cases, however, the energy requirements are lowered when 

 the oxygen is withdrawn, due to cessation of muscular 

 movements.) As to the organisms which are injured or 

 succumb, they are either incapable of gaining sufficient 

 energy through anaerobic processes, or some specialized 

 tissue in them, like the nervous tissue, is irreversibly 

 damaged, or some toxic metabolic end products accumu- 

 late in their body. 



3. Some organisms have adapted themselves to anaero- 

 bic life by excreting toxic end products, others by elabo- 

 rating, instead, substances which are relatively non-toxic. 



4. Invertebrates are capable of conditioning, in culture, 



