RESPIRATORY METABOLISM 385 



The Measurement of Anaerobic Metabolism and Glycolysis 



The measurement of anaerobic metabolism is somewhat more complex 

 than the measurement of aerobic. The standard criterion of O2 con- 

 sumption does not exist, and the auxiliary criterion of CO, production 

 indicates only the carbon which is completely oxidized. Sometimes this 

 may comprise only a small percentage of the total metabolic changes; 

 and in some cases measurements may be complicated by the presence of 

 hydrogen, methane, and other gases. Therefore we must usually attempt 

 to trace anaerobic metabolism by measuring changes in the concentration 

 of several substances in the liquid phase, instead of one or two substances 

 in the gaseous phase; and this is more difficult. In some cases it is possible 

 to give an organism a known substrate, for example, carbohydrate, and 

 to measure the decrease in the quantity of the substrate and the increase 

 in the amount of decomposition products at various intervals. From 

 carbohydrate decomposition these may be alcohols, aldehydes, and or- 

 ganic acids. From protein decomposition we might expect a wide variety 

 of nitrogen-containing amino-acid fragments, and by deaminization of 

 amino acids a wide variety of organic acids may be produced. From de- 

 composition of lipoids we may expect products somewhat similar to 

 those from carbohydrates. Methods for the final identification of these 

 compounds usually take one into the field of microanalytical biochemistry 

 (see Peters and van Slyke, 1932; Friedemann, 1938; and publications 

 by von Brand, Reiner, and others, cited below). The identification of 

 the acid formed is important in any study of the energetics of anaerobic 

 carbohydrate metabolism, because the processes which yield the various 

 acids release quite different amounts of energy. For many purposes, 

 however, it is customary, if not adequate, to measure acid production by 

 manometric measurement of the amount of COo which is released from a 

 bicarbonate buffering system, as CO2 or stronger acids are produced by 

 the organism. This gives an index of acid production, but leaves us 

 ignorant of the nature of the acid. Changes in total titratable acidity or 

 alkalinity are also used, and it seems as if, under certain conditions, 

 accurate titration curves might be obtained which would give a fair index 

 of the kind and amount of acids present. 



In metazoan metabolism it is usually assumed that oxidation of glu- 

 cose is preceded by a molecular rearrangement which results in the 

 formation of lactic acid. 



