BIOCHEMISTRY OF THE SEXUAL ORGANS 307 



the boar, and the bull have been examined/ but neither protamines 

 nor histones were found. 



The acid substance isolated from ,the spermatozoa, the nucleic 

 acid, does not show any variation in the different species and classes 

 of animals. It is, in fact, so similar to the nucleic acid present in 

 the nuclei of somatic cells, that it is now considered to be identical 

 with the nucleic acid prepared from the thymus, whicli has been 

 studied in great detail. These nucleic acids do not belong to the 

 proteins, but they exist in the cell always in combination with 

 proteins as-nucleins or as nucleoproteins, according to the amount of 

 protein present in the combination. 



The nucleic acids are dry, pulverulent, white substances of a 

 decidedly acid character, containing nine to ten per cent, of 

 phosphorus, not easily soluble in cold water, but readily dissolved 

 by alkalis or ammonia. They are precipitated from their solutions 

 by mineral acids and by alcohol. They form insoluble salts with the 

 heavy metals and with barium, calcium, and strontium. If pure, 

 they do not give the colour reactions for proteins. They rotate 

 polarised light to the right. A solution of nucleic acid, acidified 

 with acetic acid, gives a precipitate with protein solutions. By 

 boiling the watery solutions the nucleic acids are partially decom- 

 posed.^. Complete hydrolysis is brought about by treatment with 

 hot acids. The main products of hydrolysis which have been thus 

 obtained from various nucleinic acids can be grouped under five 

 headings : — 



1. Phosphoric acid. 



2. Lsevulinic acid, a substance formed by the oxidation of 

 carbohydrates, and indicating the presence of a hexose (the imcleic 

 acids from plants, yeast for instance, contain a pentose). 



3. Derivatives of purine — 



(1) N=CH (6) 



I I 



(2) HO C (5)— NH (7)\^ 



II II , >CH (8) 



N-C (4)— NH {9V 



(3) N-C (4)— NH (9) 



namely — i 



Adenine = 6- Aminopurine ; Hypoxauthine = 6-Oxypurine ; 

 Guanine=2 Amino-6 Oxypurine ; Xanthine = 2-6 Dioxypurine. 



Of these only adenine and guanine are present as such in 

 the nucleic acid molecule, while hypoxanthine and xanthine are 



1 Miescher, loc. cit, " Die Spermatozoen einiger Wirbelthiere," Histochemische 

 Arbeiten ; Mathews, loc. cit. 



^ For a complete account of the chemistry of nucleic acid see Jones, " Nucleic 

 Acids," in the series Monographs on Biochemistry, 2nd Edition, London, 1920. 



