NUCLEOTIDES I33 



reaction, since Gram-positive but not Gram-negative bac- 

 teria contain large amounts of the phosphates of various 

 polyalcohols, in particular, glycerol. If a suspension of Staph, 

 aureus is shaken with minute glass beads, the cells are dis- 

 rupted, but the outer layer of the cell — the 'cell wall' or 'cell 

 envelope' — remains intact, and it is with this that the major 

 portion of the polyol phosphates is associated [42]. However, 

 no direct evidence has yet been presented that these phos- 

 phates participate in the Gram-staining reaction. The recent 

 work of Bartholomew and Mittwer has provided further 

 support for the view that a layer immediately internal to 

 the cell wall is the site of the Gram-staining reaction [3]. 



The nuclei of plant and animal cells are rich in nucleic 

 acids, mostly of the DPNA type, and it is now generally 

 accepted that transmission of hereditable characters is 

 associated with these substances. Whether or not bacteria 

 possess a nucleus has been the subject of endless and incon- 

 clusive discussion, but they do undoubtedly contain struc- 

 tures composed of DPNA and known as chromatinic bodies. 

 The latter can be demonstrated in living cells by dark ground 

 phase contrast microscopy [50] and in dead cells by the 

 Feulgen or Giemsa staining technique. The Feulgen tech- 

 nique is based on the fact that after being subjected to acid 

 hydrolysis, deoxypentose nucleic acids, but not nucleic acids 

 of the pentose type, restore the colour of Schiff's reagent, 

 consequently cellular structures composed of DPNA be- 

 come stained magenta. Since any aldehyde is capable of 

 giving a positive reaction, the results should not be accepted 

 without confirmatory evidence. If an observed staining re- 

 action is due to PNA or DPNA, it should no longer be given 

 by material previously treated with the appropriate enzyme, 

 ribonuclease or deoxyribonuclease (p. 134), and then washed 

 (Plate III). Caution is also required in interpreting the re- 

 sults obtained in this manner since it may not be justifiable 

 to assume (i) that the enzyme can penetrate the experimental 

 material and thus come into contact with the substrate and 

 (ii) that the enzyme preparation is specific in its activity. 



Although the evidence is often indirect, , there are good 

 reasons for believing that in micro-organisms, as in the 



