THE NUCLEOPROTEIDS. 



285 



We must once more state that too much reliance should not be placed 

 upon these figures. Burian and Walker Hall 3 called attention to the fact 

 that, in the preparation of the purine bases, oxypurines (xanthine and 

 hypoxanthine) might be formed from the aminopurines (adenine and 

 guanine). As we have seen, Steudel has proved this directly. This 

 probably accounts for the fact that Schmiedeberg, in investigating salmon 

 nucleic acid, found guanine and adenine, but no xanthine nor hypo- 

 xanthin. 



Thymo-nucleic acid from the thymus gland is another nucleic acid which 

 has been investigated considerably. 4 Phosphoric acid, thymine, cytosine, 

 guanine, adenine, laevulic acid, and ammonia were obtained by hydrolytic 

 decomposition. Guanylic acid, obtained from the pancreas, broke down 

 into guanine, phosphoric acid, and a pentose. A nucleic acid has also 

 been isolated from the spleen. We may add, finally, that analogous 

 products can also be obtained from the plants. Triticonucleic 5 acid, 

 obtained from the embryo of wheat, has been most studied. It yields 

 by hydrolysis : guanine, adenine, cytosine, uracyl, phosphoric acid, and a 

 pentose. Nucleic acids have also been isolated from tubercle-bacilli and 

 from yeast. 



We cannot at present say anything regarding the nucleic acids and their 

 cleavage-products, and shall confine ourselves in the following to the dis- 

 cussion of their participation in metabolic processes. We will state, at 

 the start, that there can no longer be any doubt that the nucleo- 

 proteids are disintegrated in the cell-metabolism, and participate to the 

 same extent in the reconstruction. There is scarcely any question but 

 that the animal cell obtains the components of the nucleoproteids already 

 formed in the food. It does not seem probable that the purine and pyri- 



1 Y. Inoko: Z. physiol. Chem. 18, 57 (1894). 



8 S. Schindler: ibid. 13, 432 (1889). 



3 R. Burian and W. Hall: ibid. 38, 366 (1903). 



4 H. Steudel: ibid. 42, 165 (1904); 43, 402 (1904); 46, 332 (1905); P. A. Levene, 32, 

 541 (1901); 37, 402 (1902-03); 38, 80 (1903); 39, 4 (1903); 39, 479 (1903); 43, 199 

 (1904); 45, 370 (1905); Am. J. Physiol. 12, 213 (1905). 



5 T. B. Osborne and J. F. Harris: Z. physiol. Chem. 36, 85 (1902). 



