ANAEROBIC METABOLISM 225 



effort has so far been made to study, in these cases, what 

 fraction of the total carbon dioxide is of inorganic origin. 



Another method, much used in recent years {cf. for 

 example, Davis and Slater, 1928; Gilmour, 1941) is to 

 study the gas metabolism during recovery from anaero- 

 biosis. The accumulated metabolic end products are then 

 removed through aerobic oxidation and the bicarbonates 

 are resynthesized, a process which obviously results in 

 the retention of carbon dioxide. If the normal and the 

 posi-anaerobic respiratory quotients are determined, the 

 amount of retained carbon dioxide can be calculated. But 

 this method has the same limitation as that outlined 

 above: only if all the metabolic end products actually 

 ac3umulate in the body and are not excreted, will it give 

 reliable quantitative data concerning the origin of the 

 anaerobically produced gas. 



The reaction between inorganic substances and the an- 

 aerobically produced acids is of great biological impor- 

 tance especially if the latter are retained in the body ; it 

 works as a buffer mechanism that tends to prevent a dan- 

 gerous lowering of the pH. This point has been investi- 

 gated primarily by Collip (1920, 1921), Dotterweich' 

 and Elssner (1935), Dugal and Irving (1937, 1938), Dugal 

 (1939, 1939a) and Dugal and Fortier (1941), who have 

 shown that in clams kept under anaerobic conditions the 

 carbon dioxide content of the mantle cavity fluid, as well 

 as of the tissues themselves increases enormously. In 

 Dugal's experiments the amount of carbon dioxide rose 

 under anaerobic conditions from 6 to 150 cc. per 100 cc. 

 of mantle cavity fluid. At the same time lactic acid and 

 calcium accumulated but no decided shift in pH took place. 

 The calcium was obviously derived from the calcareous 

 shell which, in fact, became eroded. The process— which 

 in this case does not lead to free carbon dioxide-can be 

 formulated as follows : 



2CaC03+2C3H603— Ca(HC03)2+Ca(C3H503)2 



