Uridin and Cytidin Phosphoric Acid. 21 



sisting of NaCl — 1.2 per cent., CaCl — 0.025 P er cent., KC1 — 0.042 

 per cent., NaHC0 3 — 0.02 per cent. To 1,000 parts of this solu- 

 tion was added 1 part of commercial (3 per cent.) H 2 0 2 in order to 

 allow the tissue a sufficient amount of oxygen and at the same 

 time obviate the appearance of free bubbles in the specimen. 

 An increase of size of the tissue was obtained in nearly 85 per cent, 

 of the specimens. Tissues used for the present study were the 

 spinal cord and intestines of a chick embryo of 4 to 10 and 14 to 

 17 days respectively. The increase in size was pretty regularly 

 about 0.5 mm. during the first twenty-four hours, which corre- 

 sponds very nearly to the results obtained by M. R. Lewis. 



The newly grown part of the tissue has often the same thick- 

 ness as the rest of the piece, the whole piece becomes usually 

 more uniform. On the other hand in about 36 specimens in 

 which there was no growth the thickness of the tissue was 

 not uniform. Apparently then a successful growth of tissue is 

 not due to any chemical or physical phenomenon. 



Experiments are undertaken with tissue cultures in serum 

 and on influencing the growth with physico-chemical agents. 



121 (1299) 



Uridin and cytidin phosphoric acid. 



By P. A. Levene. 



[From the Rockefeller Institute for Medical Research.] 



In a series of articles published in course of the last few years, 

 Walter Jones and his co-workers advanced a theory on the mode 

 of linkage of the four nucleotides taking part in the molecular 

 structure of yeast nucleic acid. According to these authors, the 

 nucleus of yeast nucleic acid is a tetra ribose of the following 

 structure [(C 5 Hio0 8 )4 — 3H2O]. The assumption was based on 

 the isolation of three substances which the authors viewed as 

 dinucleotides, having the properties of a tetrabasic acid. In 

 a previous publication the present author expressed the view 

 that the experimental evidence adduced by Jones and co- 

 workers was not sufficient to establish their theory. It also 

 seemed to the present author that the experimental evidence pre- 

 sented was insufficient to establish the individuality of the guanosin 



