88 Microscopic Histochemistry 



tides at about the same rate/^^ Extraction of RNA with 0.1 

 N KOH is recommended by Sulkin.^^^ 



Henry and Stacey^^^ have presented excellent evidence to 

 show that the Gram-positive staining of bacteria is due to an 

 RNA-Mg complex, extractable with a 2 per cent bile salt 

 solution at 60° C. This bacterial RNA is obviously different 

 from the ordinary type of RNA, which is Gram-negative and 

 insoluble in bile salt solutions. 



b) Enzymatic procedures.— EnzymsLtic hydrolysis of nu- 

 cleic acids follows a course different from that seen in acid 

 hydrolysis. The first stage is depolymerization of a variable 

 degree; the next stage is the removal of PO4 groups; and the 

 last one is the breakdown of glycosidic linkages, which are 

 the first ones to be attacked by acids. ^'^^ It is very likely that 

 every stage has its own enzyme or enzymes ( depolymerase, 

 phosphatase, nucleosidase) and that many of the enzyme 

 preparations used in histochemistry are mixtures of several 

 components. In fact, they are often contaminated by pro- 

 teases of various kinds. This explains the different results 

 obtained by the use of enzymes prepared in different ways. 



The depolymerases of RNA and DNA are definitely spe- 

 cific; a good preparation of desoxyribonuclease will not at- 

 tack RNA and vice versa. 



According to Danielli,^^ the specificity of the nucleases is 

 open to doubt. He also questions whether the histochemical 

 application of enzymes can ever yield quantitative results, 

 since the penetration of the large enzyme molecules into the 

 interior of the section would be blocked by even a monolayer 

 of protein. However, there is ample experimental evidence 



138. Koenig, H., and Stahlecker, H.: J. Nat. Cancer Inst., 12:237, 1951; 

 Schneider, W. C: J. Biol. Chem., 161:293, 1945. 



139. Sulkin, N. M.: Proc. Soc. Exper. Biol. & Med., 78:32, 1951. 



140. Henry, H., and Stacey, M.: Nature, 151:671, 1943; Henry, H., 

 Stacey, M., and Teece, E. G.: Nature, 156:720, 1945; Henry, H., and 

 Stacey, M.: Proc. Roy. Soc. London, B, 133:391, 1946. 



141. Catcheside, D. G., and Holmes, B.: Symp. Soc. Exper. Biol., 1:225, 

 1947. 



