BAOTERIAL REDUCTIONS 99 



various enzymic activities into play. To assume that the cell can affect the medium 

 only (i) by removing free oxygen dissolved in the medium, and (ii) by liberation of 

 reducing substances from autolysed cells is to ignore a number of facts accumulated 

 from studies of bacterial metabolism. This point of view is one which is steadily 

 gaining ground amongst students of the subject. 



It is a common fallacy in the consideration of the reducing phenomena of bacterial 

 cultures to confuse symptoms with functions. The utilisation of oxygen in the culture 

 medium by bacteria is frequently regarded as a function, whereas it is nothing but a 

 symptom of the dehydrogenation of nutrient materials by the organisms in their 

 search for sources of energy. A further fallacy is to confuse bacteria with multi- 

 cellular organisms. Since higher animals eat or absorb food and excrete waste 

 products, a similar mechanism is frequently ascribed to bacteria. It is more helpful, 

 however, to regard the micro-organism as an active centre where chemical reactions, 

 catalysed by the cell enzymes, proceed near the cell surface. The conception that 

 glucose is absorbed by a bacterium, digested as in the higher animals and then 

 excreted as lactic acid requires amplification. 



It has been calculated that a single bacteriimi may break down some millions of 

 molecules of glucose in a minute. The transport problem involved in this process 

 must be considerable even when the glucose molecules have merely to be led up to the 

 cell surface and the metabolic products to be led away, but if the glucose has to diffuse 

 into the cell interior and the metabolic products have to diffuse out the movements of 

 materials must be even more intricate. Surface catalysis presents many analogies 

 to cellular enzyme effects and the difficulties involved in the assumption of a multi- 

 plicity of specific enzymes may be lessened by acceptance of the theory that reactive 

 molecules cannot react unless their configuration is such that they are absorbed at the 

 surface, and the specificity of surface orientations helps to account for the selectivity 

 of many cellular activities. The chemical material required for the building of new 

 cellular material must, presumably, penetrate the bacterial envelope and the energy 

 liberated in metabolic processes must also be available to the cell, but it would appear 

 that many aspects of the physiology of cells become clearer if the postulate be 

 accepted that many bacterial metabolic processes take place not in the cell interior 

 but at its surface or near the surface. 



The emphasis laid here on the distinction between micro-organisms and higher 

 multicellular organisms has been criticised on the grounds that this ignores the vast 

 amount of work carried out in the last decade or so showing similarities between the 

 ultimate reactions of metabolism in bacteria and animals. This, however, is not 

 intended and study of the previous two chapters will reveal the recurrence in vastly 

 different organisms of the same patterns and building stones of metabolic processes. 

 In point of fact the author claims some share of prophetic insight for the following, 

 written in 1930 for the first edition of this book : 



" Such advances in bacteriology are preliminary to advances in other realms of biology 

 where the investigator has to deal, not with many cells of the same type, but with cells of 

 countless different kinds. A fuller understanding of unicellular behaviour and its variations 

 must precede the solution of the more complex problems." 



The object then in distinguishing between the metabolic activities of bacteria 

 and animals is not to discount the similarities of the fundamental reactions but to 

 underline the differences in organisation. The tissue cell stays in situ, has brought to 



