SELECTED PAPERS 



nature of the nitrogenous foodstuffs often determines whether a par- 

 ticular substrate, hence also a particular intermediate product, will or 

 will not be further oxidized. This also reveals a very striking relation 

 between dissimilation and assimilation, and perhaps may open a way 

 for penetrating more deeply into these problems. After all, it is quite 

 remarkable that A. suboxydans can grow perfectly well in a mineral 

 medium containing a few per cent mannitol if nitrogen is supplied 

 in the form of an ammonium salt. It is thus certain that this bacterium 

 can use ammonia nitrogen for the synthesis of its proteins. But it 

 appears also that this organism does not grow in the same medium if 

 glucose is substituted for mannitol, whereas, in the presence of pep- 

 tone, glucose is very rapidly oxidized, and the bacteria then multiply 

 profusely. Glucose is therefore fully adequate as an energy-providing 

 substrate. Thus we see how two substances, each one utilizable in its 

 own function, can furnish an inadequate combination as food. Might 

 it perhaps be possible to ascribe this unexpected phenomenon to a 

 difference in the decrease in free energy of the first stages of the oxida- 

 tion of mannitol and glucose, respectively, a difference that might 

 cause ammonia nitrogen to be used for the synthesis of bacterial 

 protein in the one, but not in the other case? We don 't know; but 

 we can learn from this example that the occurrence of a biological 

 oxidation does not depend only on the nature and condition of the 

 living cells and the presence of an oxidizable substrate, but that it 

 is conditioned by very subtle modifications in the composition of the 

 medium. 



A further consideration of these problems inevitably reminds us of 

 those other phenomena of incomplete and insufficient biological oxi- 

 dations that are characteristic of the pathological deviations in the 

 metabolism of man and animals known as diabetes. Is it a tenuous 

 comparison if we say that we cure A. suboxydans of diabetes if, by the 

 addition of a small amount of peptone, we resuscitate the cells of this 

 organism, suspended in a nutrient medium that contains glucose and 

 ammonia nitrogen, and which, in view of the outcome of the experi- 

 ment with mannitol, should constitute a complete medium? And in 

 studying the beneficial but as yet rather mysterious insulin effect, is 

 there not reason to pay attention to the possibility that under the 

 influence of this hormone chemically readily detectable substances 

 may be excreted into the blood stream whose presence suffices to 



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