102 THE PHYSIOLOGY OF PROTEIN METABOLISM 



The Output of Purines. 



The ratio between the output of the purines and the total nitrogen 

 has also been used to investigate the nature and the rate of protein 

 catabolism. In the case of Beaut6 it was found that the total purine 

 (bases and uric acid) output fell at first during the fast for the first 

 three days, then gradually increased in amount until a figure slightly 

 greater than the endogenous output during the previous feeding on a 

 purine-free diet was reached. Now Nemser (297) has stated that 

 it is the nuclein part of the tissue which resists disintegration in starva- 

 tion longest, and this is not at all improbable, as the nucleins are a 

 component part of the nuclei and are therefore intimately connected 

 with cell regeneration. 



As the fast progresses there will therefore be a rise in the output 

 of endogenous purine. Apparently in starvation the body first 

 utilizes tissues which, at the time, are of least value, preserving as 

 long as possible those which are of greater importance. Thus it hap- 

 pens that in the early days of a fast the output of urinary purine (in 

 my case there was no faeces to examine) is much diminished the 

 general protoplasm, as well as the non-nitrogenous bodies, the carbo- 

 hydrates and fats forming the principal food supply, i.e. material 

 containing but little or no purine nitrogen. As the fast progresses, 

 the body can no longer obtain this material so freely, as is shown 

 by the gradual diminution in the amount of total nitrogen excreted, 

 and consequently coincident with this fall in total nitrogen, there is a 

 rise in the output of purines. This increase is probably due to the 

 fact that the body has now to draw upon its more valuable reserves 

 the nucleins, proved sources of purine supply^ to supply their quota 

 of energy along with the other tissues. Burian and Schur (81) look 

 upon the hypoxanthine of the muscle as the important source of 

 urinary purine. It may be that this hypoxanthine is the sole or 

 chief source during the early days of the fast, but as the period of 

 starvation lengthens other sources must be drawn upon. An attempt 

 (89, page 127) was made to calculate from the total nitrogen the 

 amount of endogenous purine which might be expected to be excreted. 



The table (p. 103) shows a steady decrease in the calculated amount 

 of purine nitrogen, whereas the columns giving the actual output of 

 purine nitrogen show a steady and constant rise. From these figures 

 it may be inferred, either that tissues, or parts of tissues, rich in the 

 precursors of the endogenous urinary purine are being increasingly 



