GENERAL CONCLUSIONS 169 



The importance of nucleic acids in biology is becoming increasingly evident. 

 Nucleoproteins appear to be the self-reproducing units of living matter and an 

 alteration to the nucleic acid results in a permanent alteration to the reproducing 

 units. Just as an alteration to a dye or mould will affect all the subsequent productions 

 cast in that mould so nucleic alteration affects the properties of the progeny of the 

 cell or nucleoprotein molecule. 



Apart from the range of reducing activities, other differences can be traced 

 between different organisms. With some organisms, such as pneumococci, the 

 level of reducing intensity reached is not maintained after the logarithmic phase of 

 growth ; but, on the other hand, highly oxidising conditions are gradually established. 

 This is associated with the peroxide-forming function of these organisms and is a very 

 characteristic property. The measurement of electrode potentials has proved of 

 value in the study of peroxide formation by bacteria, and of the protective effect of 

 the presence of catalase. ' 



An apt quotation appears in a paper by Wieland : " The living cell is no furnace 

 wherein all materials may be indiscriminately oxidised." Some substances may 

 be utihsed by one organism and not by another, hence differentiation of organisms 

 may be accomplished by studying the development of reducing conditions in the 

 presence of different possible nutrient materials, as in the Thunberg vacuum-tube 

 method. The most probable explanation of the differences encountered between 

 different organisms seems to lie in their possession of different enzymes. It seems likely 

 that systematic classification of organisms will result from studies of oxidation- 

 reduction conditions in bacterial cultures. 



The recognition of the effect of cultural conditions on the electrode potentials 

 of bacterial cultures is leading to a wider problem, that of the relation between 

 the oxidation-reduction conditions under which the cell is grown and its consequent 

 biological behaviour. For example : hsemolytic streptococci are frequently extremely 

 virulent when isolated from the blood stream of infected patients or animals, but when 

 sub-cultured in broth in the ordinary way the organisms lose their virulence. The 

 virulence may, however, be maintained by sub-culturing : — 



(1) In broth to which blood-serum has been added ; 



(2) In aerated broth cultures. 



The maintenance of virulence is effected by opposing the reducing effects of 

 'the organisms, by increasing their oxygen supply and this postulate is supported 

 by the measurement of electrode potentials of cultures of hsemolytic streptococci. 

 Both in serum-broth and aerated broth cultures the potential is prevented from 

 falling to the low level reached in plain broth. 



Furthermore, the matt form of haemolytic streptococci may be transformed into 

 the glossy variant at the high electrode potential produced by hydrogen-peroxide. 

 This effect has been traced to two factors, the inhibition of proliferation of the matt 

 form by the peroxide, and auto-sterilisation of the matt form, on solid media, by 

 production of peroxide by the organisms themselves. 



The mechanism of the effect is now apparent for the loss of virulence is due to the 

 proteolytic effect of an enzyme produced by haemolytic streptococci. This proteinase 

 which digests the specific substance present in virulent organisms, requires reduced 

 sulphydryl groups for its activation and under conditions of high oxidation-reduction 



