THE NUCLEOPROTEIDS. 287 



bases. Tichomiroff l has shown that hibernating insect eggs contain only 

 traces of purine bases, while the maturing eggs show a much larger per- 

 centage of these. A. Kossel 2 finally showed that the yolks of unincubated 

 eggs contained practically no purine bases. After fifteen days' incubation 

 larger amounts of guanine and hypoxanthine could be detected. We must 

 also refer to the work of Burian and Schur. 3 They estimated the amounts 

 of bases present in new-born animals, and compared these values with 

 those obtained from older sucklings. Although the latter had received 

 almost no purine bases with their nourishment, the milk, the amount of 

 these substances continually increased. Finally, we must remember the 

 work of F. Miescher, 4 who found that even the salmon, during the fasting 

 period when it remains in fresh water, not only builds up nucleins from the 

 simplest components, but newly forms the purine bases as well. All these 

 important observations show us what difficult syntheses the animal cell is 

 capable of effecting. There does not seem to be any reason for doubting 

 that the most varied constituents of the tissues of the animal organism are 

 built up of the simplest components. It is still an open question regarding 

 the manner in which the growing organism carries out this process. 



It is, at present, impossible to make any definite statements concerning 

 the products utilized in the synthesis of the purine bases. It is indeed 

 possible that further investigations with histidine and its behavior in the 

 animal organism may give us some clew to this process. This albuminous 

 cleavage-product, as we have seen, is very probably an a-amino-/?-imid- 

 azole-propionic acid: 



CH NH 



C N 



CH 2 



CH . NH 2 



COOH 



If this be true, we have another bridge from the proteins to the purines. 



We specifically call attention to our ignorance of the relations of the 

 nucleic acids to the general metabolism, because recent investigations 

 on the disintegration of these substances in the tissues have indicated 

 the ease with which these gaps in our knowledge may be overlooked. 

 They immediately become apparent when we attempt to explain the 



1 A. Tichomiroff: Z. physiol. Chem. 9, 518 (1885). 



2 A. Kossel: Z. physiol. Chem. 10, 248 (1886). 



3 R. Burian and H. Schur: ibid. 23, 55 (1897). 



4 F. Miescher: Arch, exper. Path. Pharm. 37, 100 (1896). 



