220 SECTIONAL ADDRESSES 



But there is also the possibility that the rate of sugar breakdown is 

 affected by oxygen. According to F. F. Blackman's analysis of the 

 observed data of respiratory activity of apples in air and pure oxygen, 

 there is evidence that the rate of production of the active substrate for 

 glycolysis from stable sugar is increased with increase in oxygen con- 

 centration. J. K. Scott and I have obtained what may be further evidence 

 of the possibility of this from a consideration of the relationships of 

 respiration to surface and volume in bulky tissues. Here, owing no 

 doubt to the low oxygen tension in the middle region of such tissues, 

 there is a low rate of respiration, although there may actually be no 

 indication of anaerobic respiration. The observed results can be ex- 

 plained on the view that the low oxygen tension induces a minimum rate 

 of production of the active substrate and so limits the rate of respiration. 

 It may be noted, as a corollary to this view, that the anaerobic respiration 

 usually observed after a period of aerobic respiration should gradually 

 fall to a lower level owing to oxygen shortage bringing about a lessening 

 in the rate of production of active substrate. Investigations on the 

 quantitative relations between aerobic respiration and anaerobic respira- 

 tion have made it clear that this is what generally happens, so that it is 

 frequently difficult, or indeed impossible, to fix a value for the rate of 

 anaerobic respiration, since this undergoes changes with time, sometimes 

 rising at first, but always subsequently falling. Researches carried out in 

 my laboratory by J. K. Choudhury indicate, however, that there may be 

 exceptions to this rule. 



From the course of anaerobic respiration it is, however, often possible 

 to calculate the initial rate of anaerobic respiration at the moment 

 when the material is first transferred to an atmosphere of nitrogen before 

 secondary effects have come about. This was done by F. F. Blackman 

 and P. Parija in their well-known work on the respiration of apples, 

 and they showed that the output of carbon dioxide at the beginning of 

 a period in nitrogen was actually greater in this case than the output of 

 carbon dioxide in air immediately before transference to nitrogen. From 

 a very careful analysis of the experimental data, Blackman concluded 

 that in respiration in air a large amount of some substance is formed along 

 with the carbon dioxide and water and that this substance does not 

 accumulate but is built back into the stream of katabolites. There is no 

 evidence yet to show whether this substance is actually built back into 

 sugar as Wortmann supposed to be the case in the broad bean, or whether 

 some intermediate substance of the breakdown is formed. It is important 

 to note, however, that here also evidence of an anabolic process linked 

 with the breakdown is obtained, a process called by Blackman oxidative 

 anabolism since it is dependent on the presence of oxygen. Similar 

 evidence for the existence of oxidative anabolism in storage tissues such 

 as potato tuber and carrot root has been obtained in long series of 

 experiments carried out in my laboratory by W. Leach, J. K. Choudhury 

 and J. K. Scott. 



It is more than likely that the investigation of the organic acid meta- 

 bolism of plants may shed light on our problem. It is well known that 

 in many plants, notably in succulents, but in many non-succulents as 

 well, organic acids such as malic, citric and oxalic, are present in con- 



