Studies in Pyrimidine Metabolism. 179 



heart and its relation to the thorax. If the results in these two 

 human cases are corroborated repeatedly by similar findings in 

 other instances, it is possible that the usually accepted electro- 

 cardiographic interpretation of right and left bundle branch block 

 may have to be revised. 



95 (1555) 



Studies in pyrimidine metabolism. 



By D. Wright Wilson (by invitation). 



[From the Laboratory of Physiological Chemistry, Johns Hopkins 

 University, Baltimore. \ 



By partial hydrolysis of yeast nucleic acid, preparations con- 

 taining pyrimidines as the only nitrogenous constituents were 

 prepared and administered to rabbits. Uracil nucleoside when 

 administered per os, subcutaneously or intraperitoneally caused 

 an increased excretion of urea often much more than enough to 

 account for the nitrogen administered. The undetermined 

 nitrogen (the difference between the total nitrogen and the urea 

 nitrogen) was always increased. A part of the increase in the 

 undetermined nitrogen was due to the excretion of free uracil 

 which was isolated in pure crystalline form. As much as 20 

 per cent, of the uracil fed as the nucleoside was recovered free in 

 the urine. 



When a mixture of cytosine and uracil nucleosides was admin- 

 istered to rabbits, there was an increased excretion of urea and 

 usually no increase in the undetermined nitrogen. Uracil was 

 isolated from the urine of one animal and was barely detected by 

 a color reaction in another. No increase of creatine, creatinine, or 

 purines was detected after feeding either preparation. Not even 

 a color reaction for pyrimidines was obtained by using the same 

 procedures on the urine obtained after feeding yeast nucleic acid. 



Mendel and Myers were unable to find a trace of pyrimidine in 

 the urine after feeding yeast nucleic acid but found that uracil, 

 when fed, was excreted unchanged. Taken together, the data 

 show that increasing quantities of uracil appear in the urine as 

 simpler complexes containing the uracil group are fed. The con- 



