UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



this incessant utilization of chemical energy and the other side of 

 metabolism, viz., the assimilation, or the production of new cell con- 

 stituents. 



In contemplating this possibility the problem arises whether such 

 a situation should not be apparent if one were to succeed in reducing 

 the extent of assimilation by a microbe to a minimum, so that the 

 visual new-formation of cell material, i.e. multiplication, is excluded. 

 We then encounter the problem whether it is possible to maintain 

 microbial cells alive by the supply of a food ration that will just prevent 

 multiplication. Rubner [191 3] has made an attempt at experimentally 

 testing this possibility with yeast, and had concluded that it does not 

 exist. One may, however, raise serious objections against the tech- 

 nique he used, so that we can only state that in the realm of microbes 

 this fundamental problem is still unsolved. 



But even in those cases where visual growth fails to take place we 

 must always count with the occurrence of a process of replacement of 

 worn-out cell materials, so that it remains possible to regard the 

 function of dissimilation as one serving assimilation. On the other 

 hand it is patently true that at least part of the dissimilatory energy is 

 indispensable for assimilation whenever we can ascertain that the 

 latter is accompanied by an obvious increase in energy. A good exam- 

 ple of such a situation is provided by the autotrophic bacteria which 

 produce organic matter, such as bacterial protein, from carbon diox- 

 ide. In the case of such organisms, sometimes improperly designated 

 as chemosynthetic, the microbiologists have consequently been wont 

 to stress the energy-providing reactions. 



If it is remembered, however, that experience has shown how, for 

 example, the sulphur bacteria must oxidise 32 g of sulphur to sul- 

 phuric acid in order to fix 1 g of carbon in the form of bacterial cells 

 (dissimilation process 10, Table I), it is immediately apparent that 

 the autotrophic bacteria, too, retain only a small fraction of the 

 dissimilatory energy in the form of assimilation products. This point is 

 still more obvious in the case of microbes that depend on organic 

 nutrients. Rubner's calorimetric measurements have shown convinc- 

 ingly that the autolysis of yeast cells, like most enzymatic hydrolyses, 

 proceeds with a very small heat production. Conversely it must there- 

 fore be true that the formation of yeast cells from the products of auto- 

 lysis implies an equally small energy fixation. Nevertheless, the energy 



