488 J. BRACKET 



tein silk. During blood cell formation, there is a steady decrease of the 

 PNA content partly associated with the endocellular synthesis of hemo- 

 globin (Thorell^^). While endocrine glands are relatively poor in PNA, it 

 is a striking fact that stimulation of hormonal secretion in the pituitary is 

 linked with a marked increase in the PNA content (Desclin,^" Herlant^') ; 

 more recently, Abolins^- also concluded that hormone synthesis in the 

 anterior pituitary is related to the amount of PNA present in the cells. In 

 the liver, the PNA content markedly decreases in fasting animals, a fact 

 which will be discussed later. 



There is thus no doubt that the PNA content of various cells can be 

 made to vary under different physiological conditions, but always in rela- 

 tion to protein synthesis. Some still more recent work points towards the 

 same direction: during spermatogenesis, protein and PNA synthesis are 

 closely linked together, while DNA synthesis is independent of protein 

 increase (Schrader and Leuchtenberger^^) . In the salivary gland of Dro- 

 sophila larvae, PNA content is directly related to the intensity of secretion : 

 both increase or decrease together (Lesher^^). According to Rabinovitch 

 et al.,^^'''^ a positive correlation between PNA content and protein synthesis 

 is found in the seminal vesicles of rats injected with testosterone propionate, 

 as well as in the salivary glands after ligature of the excretory ducts. 

 Finally, in the giant unicellular alga Acetabidaria mediterranean the PNA 

 content of the nucleolus markedly decreases when the organism stops grow- 

 ing after it has been left in the dark for some weeks (Stich"). 



This series of examples, which is by no means exhaustive, should suffice to 

 prove that we are really dealing with a very general phenomenon, occurring 

 in all living organisms. We shall now find out whether the cytochemical 

 evidence is confirmed by quantitative chemical analyses of PNA from 

 different biological sources. 



h. Quantitative Evidence 



A large number of independent investigations, which could hardly be 

 completely and adequately reviewed here, show clearly that there is a good 



*' B. Thorell, "Studies on the Formation of Cellular Substances during Blood Cell 



Production." H. Kimpton, London, 1947. 

 ^0 L. Desclin, Compt. rend. soc. biol. 133, 457 (1940). 

 "M. Herlant, Arch. biol. (Liege) 54, 225 (1943). 

 " L. Abolins, Eiptl. Cell Research 3, 1 (1952). 



" F. Schrader and C. Leuchtenberger, Exptl. Cell Research 1, 421 (1950). 

 '^ S. Lesher, Exptl. Cell Research 2, 577 (1951). 



'^ M. Rabinovitch, L. C. U. Junqueira, and H. A. Rothschild, Science 114, 551 (1951). 

 '* M. Rabinovitch, H. A. Rothschild, and L. C. U. Junqueira, J . Biol. Chem. 194, 



835 (1952). 

 " H. Stich, Z. Naturforsch. 6b, 319 (1951). 



