INTRODUCTION 5 



school^^"*^ with the quantitative ultraviolet spectrophotometric technique 

 [Chapter 17] led to the detection of the presence of high concentrations of 

 pentose nucleotides or pentose polynucleotides in the cytoplasm of rapidly 

 proliferating cells such as sea urchin eggs, the spinach root-tip periblem cell, 

 the imaginal disks of larvae of Drosophila melanogaster, ^^' " embryonic 

 tissues,**'^* tumor tissues,^^ and the cells of actively secreting glands.^" 

 From all these results Caspersson"** concluded that a high concentration of 

 pentose nucleic acid was characteristic of cells in which rapid protein syn- 

 thesis was taking place, either for growth or for secretion. 



These conclusions, based on histochemical and spectrophotometric meth- 

 ods, were confirmed for embryonic tissues in 1943 by Davidson and Way- 

 mouth,^' • ^2 who showed by chemical methods that pentose nucleic acid was 

 abundant in a large number of tissues in the sheep embryo and more abun- 

 dant than deoxypentose nucleic acid in many. The pentose nucleic acid, 

 however, was not peculiar to embryonic tissues for it was also found in a 

 corresponding series of adult tissues. Although the total nucleic acid was in 

 most cases higher in the embryo than in the adult, the amount of pentose 

 nucleic acid relative to deoxypentose nucleic acid varied from tissue to tis- 

 sue and was of the same order in embryonic as in the corresponding adult 

 tissue. The pentose nucleic acid of sheep liver was isolated in 1944 and 

 shown to be present in liver tissue in the surprisingly large proportion of 3 

 or 4 times as much pentose nucleic acid as deoxypentose nucleic acid.^'* 

 Its sugar was identified conclusively as D-ribose.*'' Since then, pentose nu- 

 cleic acids have been isolated from many animal tissues. Their properties 

 and the methods of isolation are discussed in Chapter 1 1 . The deoxypentose 

 nucleic acids are discussed in Chapter 10. 



Although the nucleic acids were originally thought to be essentially nu- 

 clear constituents, the occurrence of the pentose type in the cytoplasm was 

 suspected as long ago as 1905." In deciding the location of the nucleic acids 



" T. Caspersson, Skand. Arch. Physiol. 74, suppl. 8 (1936). 



**T. Caspersson, J. Roy. Microscop. Soc. 60, 8 (1940). 



" T. Caspersson, Naturwissenschaften 29, 33 (1941). 



« T. Caspersson and J. Schultz, Nature 143, 602 (1939). 



" T. Caspersson and J. Schultz, Proc. Natl. Acad. Sci. U. S. 26, 507 (1940). 



^8 T. Caspersson and B. Thorell, Chromosoma 2, 132 (1941). 



" T. Caspersson, C. Nystrom, and L. Santesson, Naturwissenschaften 29, 29 (1941); 



Acta Radiol, Suppl. 46, (1942). 

 '" T. Caspersson, H. Landstrom-Hyden, and L. Aquillonius, Chromosoma 2, 111 



(1941). 

 " J. N. Davidson and C. Waymouth, Nature 152, 47 (1943). 

 ^^ J. N. Davidson and C. Waymouth, Biochem. J. 38, 39 (1944). 

 " J. N. Davidson and C. Waymouth, Biochem. J. 38, 379 (1944). 

 " J. N. Davidson and C. Waymouth, Biochem. J. 38, 375 (1944). 

 " S. P. Beebe and B. Shaffer, Am. J. Physiol. 14, 231 (1905). 



