BIOCHEMISTRY OF THE SEXUAL ORGANS 295 



Of these cytosine and thymine are present as such in the 

 nucleic acid molecule, while uracil is formed from cytosine by 

 a secondary reaction in the process of the splitting up of the 

 nucleic acid. 



Reference has already been made to the fact that in the 

 salmon the material for the growth of the testis is supphed 

 by the muscle undergoing atrophy. The analogy existing 

 between the glycophosphoric acid which forms the " skeleton " 

 of the nucleic acid, and the glycerophosphoric acid which 

 forms the skeleton of phosphorised fats, suggests that the 

 glycerophosphoric acid present in the muscle as phosphorised 

 fat furnishes the material from which the glycophosphoric acid 

 bound up in the testis as the nucleic acid is formed. This 

 view is supported by the fact ^ that, during the period of the 

 growth of the testis, the blood of the salmon is exceptionally 

 rich in phosphorised fats, and that the tail of the spermatozoon 

 is also very rich in phosphorised fats. It would appear that 

 these substances, after having been transported to the testis, are 

 there built up partly into the nucleus of the spermatozoon, 

 while part remains accumulated in the tail of the spermatozoon 

 as reserve material. 



The origin of the purine and pyrimidine derivatives which 

 form part of the nucleic acid molecule is as yet obscure. In 

 the case of the developing ovum it has been shown (see p. 269) 

 that the hving cell has the power of synthesising these sub- 

 stances. But the substances which supply the material for their 

 formation, and the reactions which lead to it, have not yet been 

 revealed. 



The substances detailed above represent all the constituent 

 parts of the nucleic acid molecule, so that it is possible to recon- 

 stitute the nucleic acid from the products of its decomposition. 

 According to Steudel,^ the process of hydrolysis may be expressed 

 by the following equation : — 



C43H5rNi603oP4 + 4H2O = CsH.N^O + C^H^N^ + O^HsN.O, + C.H^NjO 



Nucleic acid. Guanine. Adenine. Thymine. Cytosine. 



+ C24H44O30P4. 



' Miescher, loc. cit. 



' Steudel, " Die Zasammensetzung der Nukleinsauren aus Thymus u. aus 

 Heringsperma," Zeitschr.f. phya, Ghemie, vol. liii., 1907. 



