132 OXIDATION-REDUCTION POTENTIALS 



It seems probable that nucleic acids may be the guide or skeleton on which 

 protein and enzyme syntheses occur ; always when reproduction occurs nucleic acids 

 are found, as their name implies, at the nucleus. 



The Gram-positive bacteria are fairly sharply differentiated from the Gram- 

 negative. The differentiation is effected by a staining reaction. The organisms are 

 first stained with crystal violet, then treated with a solution of iodine and finally 

 washed with alcohol. In the case of Gram-negative organisms the alcohol 

 washes out the dye, but in Gram-positive organisms the dye is retained. It is found 

 that there are marked differences in the behaviour of the two classes of bacteria in 

 their sensitivity to inhibiting agents, etc. 



The cause of this difference in Gram-staining has now been traced to the presence 

 of ribonucleic acid in Gram-positive organisms. Henry and Stacey have shown that 

 when treated with bile salts in the presence of oxygen the magnesium salt of ribose 

 nucleic acid is removed from the cells which then no longer retain the Gram-stain. 

 The enzyme ribonuclease also removed the Gram-staining complex. Furthermore, if 

 the cells were kept reduced by formaldehyde they could then be re-plated by mag- 

 nesium ribonucleate from the same or some other source and thus became Gram- 

 positive again. Gram-negative organisms are found to contain a much smaller 

 proportion of ribonucleic acid and they cannot be plated with magnesium ribonu- 

 cleate to become Gram-positive. Presumably the proteins near the surface of Gram- 

 positive organisms have groups orientated to combine with the ribonucleic acid. 



Another interesting function of nucleic acids in bacteria, this time in the case of 

 pneumococci, has now been tracked down. It was shown by Grifl&th over 20 years 

 ago that when R t}'pe II pneumococci which had lost their capsules and type-specific 

 substance were inoculated into a mouse with some heat-killed capsulated Type I 

 pneumococci, the organisms recovered after the infection were smooth Type I 

 capsulated pneumococci. This change-over of type-specific substance was later 

 carried out in vitro. Avery, MacLeod and McCarty (1944), have now succeeded in 

 effecting this type transformation by adding purified desoxyribosenucleic acid from 

 Type III pneumococci to non-capsulated Type II cells, which then became Type III 

 cells and remained so on sub-culture. Again a nucleic acid has shown itself to be an 

 organiser of synthesis. Once the cells were presented with the pattern of nucleic 

 acid subsequent generations of cells continued to synthesise it and in turn the nucleic 

 acid being present controlled the synthesis of the capsular polysaccharide. 



SOILS, SEWAGE AND SEA-WATER 



A considerable amount of work has been reported on oxidation-reduction 

 potential studies on soils especially with regard to orchards and tea-gardens and 

 the decomposition of vegetable matter. (Buchler, Martin and Parks, 1939 ; Burrows 

 and Cordon, 1936 ; Cummings and Reed. 1940 ; Darnell and Eisenmenger, 1936 ; 

 Dirks, 1940; Heintze, 1935; Keaton, 1938; Pearsall, 1938; Peech and Batjer, 

 1935; Volk, 1939; Stephenson, Schuster and Spulnik, 1938; Sturgis, 1936.) 



Oxidation-reduction potential changes in sewage and sludges are reported by 

 Dickinson, (1940), Moore (1942). 



Hood (1948) has examined the oxidation -reduction potentials at the various stages 

 of sewage purification and points out the differing potentials reached in sedimentation 

 tanks under varying conditions (Fig. 37). 



