AXAEROBTC METABOLISM 199 



Szent-Gyorgy (1939), however, pointed out that this trans- 

 fer of oxygen is only a final result which cannot be 

 achieved directly. It is attained, as he expresses it, by 

 ''taking off and putting on H, taking off water and put- 

 ting it on again" in a complicated series of steps which, 

 in the case of the lactic acid fermentation, involves triose 

 — glyceric acid — enol pyruvic acid — pyruvic acid and the 

 participation of cozymase. Szent-Gyorgy suggests that 

 these shifts of the hydrogen atoms are of paramount im- 

 portance in the actual liberation of energy. 



The main reactions in which carbohydrates are utilized 

 anaerobically by invertebrates are: (A) lactie acid fer- 

 mentations, (B) fatty acid fermentations and (C) mixed 

 fermentations in which lactic, fatty and dibasic acids as 

 well as alcohol may be formed and in which at least two 

 of these substances appear. These possibilities will be 

 discussed separately in the following sections. 



A. Lactic acid fermentation. Lactic acid fermentation 

 is one of the best-known anaerobic processes occurring in 

 animals. It has been studied intensively in vertebrates 

 where it is, in fact, the only definitely known way of car- 

 bohydrate utilization under anaerobic conditions. It is 

 usually designated as glycolysis and the present writer 

 feels that this term should be reserved only for this one 

 process and should not be applied, as is done by some au- 

 thors, to other types of carbohydrate fermentations. 



It was pointed out previously that investigators some- 

 times assume the formation of lactic acid in invertebrates 

 without actually having demonstrated it. They take for 

 granted that there is only one type of anaerobic carbo- 

 hydrate utilization, namely, true glycolysis. Such an as- 

 sumption may lead to erroneous, or at least insecure con- 

 clusions, as a brief review of some cases will show. 



Von Fenyvessy and Reiner (1924, 1928) as well as Gei- 

 ger, Kligler and Comaroff (1930) believe that a true gly- 

 colysis occurs in the metabolism of trypanosomes. Von 

 Fenyvessy and Reiner draw this conclusion from the ob- 



