226 ANAEROBIC METABOLISM 



If isolated tissues of Anodonta hallenbeckii are em- 

 ployed for experiments on anaerobiosis, a buffer action, 

 similar in principle to the one just described, can be ob- 

 served. It seems, however, that calcium carbonate plays 

 here only a minor role. The chief buffer is another cal- 

 cium compound, perhaps a calcium proteinate ( Culbreth, 

 1941). Dotterweich and Elssner (1935) assumed the ex- 

 istence of a similar organic buffer in the case of Anodonta 

 cygnea, where, however, it is of less importance than the 

 inorganic buffer mechanism. 



Deposits of calcium salts can probably be used in a 

 comparable manner in other invertebrates. Thus, it has 

 been suggested that the calcareous corpuscles of tape- 

 worms may serve as an alkaline reserve (von Brand, 

 1933a). A similar function may be ascribed to the cal- 

 ciferous glands of earthworms. It has, in fact, been 

 shown that these are used to buffer the carbon dioxide 

 that accumulates under certain conditions in the body 

 fluids of the worms (Dotterweich, 1933), but whether 

 they serve also under anaerobic conditions to buffer 

 organic acids is not yet know^n. 



B. Liberation of carbon dioxide from organic sources. 

 It is obvious that no carbon dioxide is produced directly 

 from carbohydrates when the latter undergo lactic acid 

 fermentation. In animals showing only this type of 

 metabolic process, therefore, all the carbon dioxide found 

 under anaerobic conditions must be derived from the 

 neutralization of the acid. The quantitative investigations 

 of Dugal (1939) on Venus mercenaria agree with this con- 

 clusion, although earlier experiments of Berkeley (1921) 

 and of Collip (1920, 1921) on clams seemed to indicate 

 that at least some carbon dioxide originated from metab- 

 olic processes proper. One should, of course, remember 

 that, in anaerobically kept animals, proteins and in excep- 

 tional cases even fats may be consumed besides carbohy- 

 drates and that some carbon dioxide may be derived 

 from these sources. 



