224 ANAEROBIC METABOLISM 



ed by the control allow one to calculate the carbon dioxide 

 set free by organic acids during the experiment. In 

 many cases, however, another fraction of carbon dioxide 

 appears in the experimental vessel, namely, carbon diox- 

 ide originating directly from the degradation of organic 

 material. In order to determine the magnitude of this 

 fraction, one subtracts the total carbon dioxide pressure 

 due to bicarbonates from the total carbon dioxide pres- 

 sure (after acidification) actually observed in the experi- 

 mental manometer, since this latter pressure is a result- 

 ant of the pressures of both fractions. This priDcedure, 

 for the details of w^hich the reader is referred to Dixon 

 (1943), can conveniently be employed with small animals, 

 like protozoa, or with tissue slices, but it obviously can- 

 not be carried out with large experimental animals. 



With the latter, one can determine the amount of lac- 

 tic acid that has accumulated in the body during the anoxic 

 period. Since one is fairly safe in assuming that the 

 acids stored in the tissues w^ll be almost entirely neutral- 

 ized, one can calculate the amount of carbon dioxide set 

 free during neutralization. In order to determine wheth- 

 er all the carbon dioxide excreted during the experimen- 

 tal anaerobic period is of this origin, or whether a cer- 

 tain amount was formed directly from organic material, 

 it is only necessary to compare the calculated amount with 

 that actually found during the anoxic period ; any excess 

 in the latter indicates that carbon dioxide originated also 

 from the breakdown of some organic food substance. It 

 must be emphasized that this procedure will yield reli- 

 able results only if the organic acids remain stored in the 

 body as long as the oxygen is missing; if they are ex- 

 creted, matters become more complicated, because the 

 acids are not always neutralized before being eliminated. 

 It can be demonstrated readily that much of the acid 

 present in a saline in which parasitic worms were kept is 

 in the free state ( cf. von Brand, 1933a and 1938a, for the 

 acids produced by Moniezia and Eustrongylides) . No 



