I I. LESLIE 



New methods of expressing results have come into use in recent years. 

 Since Boivin, et al? and subsequent investigators estabhshed that there is 

 a constant average amount of DNA per nucleus for any animal tissues 

 (Chapter 19), DNA has become a useful standard of reference for revealing 

 the changes in cell number and cell composition and has been used in this 

 capacity by a number of authors.^'^^ In cases where it has been possible to 

 compare results as expressed in amount per organ, amount per average cell, 

 and concentration per unit weight of tissue, it has become clear that the 

 last method of expression, which is the one most commonly employed, can, 

 in certain circumstances, be completely misleading. '*■ ^^ 



However, it is essential to study various aspects of tissue composition 

 simultaneously. In this review an attempt has been made to obtain as far 

 as possible from published results the amounts of PNA and DNA in terms 

 of content per organ, concentration per unit of fresh weight, concentration per 

 unit of protein nitrogen, amount per average cell, and the ratio PNA/DNA. 



It has been disappointing to find so little information on the direct quan- 

 titative relationship between nucleic acids and protein in tissues in view of 

 the widely accepted association between these components. Information 

 about the content of nucleic acids in tissues is, of course, insufficient evi- 

 dence on which to come to a final conclusion about their function. To illus- 

 trate the difficulties, one need only mention the finding of Munro ei al}^ 

 that, whereas an increase in energy intake would not increase the content of 

 liver PNA on a protein-free diet, it significantly raised the uptake of P'^ 

 by PNA. 



II. Methods 



Determinations of the nucleic acids are usually based on (1) their phos- 

 phorus content, after separation of PNA and DNA, (2) the pentose of PNA 

 and the deoxypentose of DNA (see Chapter 9), or (3) the ultraviolet ab- 

 sorption in the region 357 to 270 mju of the purine and pyrimidine compo- 

 nents (see Chapter 14). The last two methods are more specific than the 

 first, but it is important to select suitable samples of PNA and DNA as 

 standards, since the proportions of purines to pyrimidines vary according 



' A. Boivin, R. Vendrely, and C. Vendrely, Com-pt. rend. 226, 1061 (1948). 



« R. Bieth, P. Mandel, and R. Stoll, Comvt. rend. soc. hiol. 142, 1020 (1948). 



« J. N. Davidson and I. Leslie, Nature 165, 49 (1950). 

 '» J. N. Davidson and I. Leslie, Cancer Research 10, 587 (1950). 

 " R. M. Campbell and H. W. Kosterlitz, /. Endocrinol. 6, 308 (1950). 

 >2 J. M. Price and A. K. Laird, Cancer Research 10, 650 (1950) . 

 1' I. Leslie and J. N. Davidson, Biochim. et. Biophys. Acta 7, 413 (1951). 

 '* R. Y. Thomson, F. C. Heagy, W. C. Hutchison, and J. N. Davidson, Biochem. J. 



53, 460 (1953). 

 i*H. N. Munro, D. J. Naismith, and T. W. Wikramanayake, Biochem. J. 54, 198 

 (1953). 



