AX AEROBIC METABOLISM 203 



as very young animals did. Curiously enough, Dugal 

 and Fortier (1941) insist that the organic acid produced 

 by oysters is not lactic acid, but another as yet uniden- 

 tified acid. In Venus, on the other hand, rather large 

 amounts of lactic acid are formed under analogous con- 

 ditions (Dugal, 1939, 1939a). 



A few other cases have been described in which lactic 

 acid is the only identified organic end product resulting 

 from anaerobic metabolism, but they are all open to ques- 

 tion. These instances will be reviewed briefly here al- 

 though in the future they will probably have to be clas- 

 sified among mixed fermentations. 



Slater (1927), working with cockroaches kept under 

 anaerobic conditions, found a much smaller accumulation 

 of lactic acid than was to be expected on the assumption 

 that the gas metabolism during recovery involved the re- 

 moval of lactic acid. In one series of experiments, for 

 example, the amount measured was 80 mg. per 100 g., 

 the expected one 540 mg. Gilmour (1941) found also that 

 whereas Tenebrio larvae consumed 0.9 mg. of carbohy- 

 drate per gram of body tissue per hour during anaero- 

 biosis, only 0,15 to 0.40 mg. of lactic acid was formed, i.e., 

 maximally, less than 50 per cent of the expected amount. 



Finally, a few words may be said about the interme- 

 diate processes occurring during lactic acid fermenta- 

 tion. The chain of reactions leading from carbohydrate 

 to lactic acid has been thoroughly studied for micro-or- 

 ganisms and vertebrate muscles ( cf. summaries by Kahn, 

 1932; Parnas, 1937; Meyerhof, 1937 and Stephenson, 

 1939). So far, not a single study has been made with in- 

 vertebrates that exhibit pure glycolysis and only very few 

 with animals in which lactic acid is formed along with 

 other acids, that is, in which the fermentations are of the 

 mixed type. Thomas (1942) assumes that lactic acid 

 formation in Tetrahymeua follows the same pattern as 

 in vertebrates but he does not adduce direct evidence (iso- 



