152 TRANSITION TO ANAER0BI08IS 



It is clear that a respiratory quotient in excess of 1 

 demonstrates the production of carbon dioxide that is 

 not derived from aerobic processes. But the mere fact 

 of a surplus carbon dioxide production does evidently 

 not warrant any further conclusion as to the chemical 

 nature of the anaerobic processes going on. The carbon 

 dioxide may be derived directly from the metabolized 

 substances, or it may be liberated from bicarbonate or 

 other inorganic substances through acids formed during 

 the fermentative metabolism. It will frequently be of 

 mixed origin and its attribution to a definite reaction is 

 a problem which has apparently not yet been studied ex- 

 perimentally in cases in which fermentations induced by 

 a partial lack of oxygen proceed simultaneously with 

 aerobic oxidations. We shall return to this problem 

 later in discussing purely anaerobic metabolism. 



D. Accumulation of an oxygen debt. Lund (1921) in- 

 vestigated this question, using Planaria agilis. He found 

 as mean values of one of his series, that the oxygen con- 

 sumption in well-aerated water (5.25 cc. of oxygen per 

 liter) was 282 cc. per 100 g. per 24 hrs.; in water con- 

 taining only 0.25 cc. of oxygen it was 37 cc. per 100 g. 

 per 24 hours, and finally, during recovery in water with 

 an oxygen content of 5.40 cc. per liter it amounted to 

 492 cc. per 100 g. per 24 hrs. Considerable variations 

 were observed in individual experiments, the increase 

 varying from 2 to 85% over the normal rate. Curiously 

 enough it was not proportional to the time of exposure 

 to partial asphyxiation, but was rather related to the 

 physiological state of the worms : the increase being more 

 pronounced in starved than in fed animals. Whether 

 planarians are able to excrete some of the non-oxidized 

 substances — this might explain some of Lund's contra- 

 dictory results — has not yet been investigated. 



It is quite obvious that no oxygen debt will accumu- 

 late if an organism eliminates all waste products through 



