INTRODUCTION 19 



high velocity of creatine combustion in health. The creatinine 

 of the urine only represents a small fraction of the creatine 

 formed in the organism. The uric acid output in the dog appears 

 constant, as in this animal the oxidation of purin derivatives is 

 exceedingly high, so that only a minimal amount escapes in the 

 urine as uric acid. However, as soon as the liver is excluded 

 from the circulation, and the intensity of the purin oxidation is 

 diminished, the uric acid output in the dog begins to show marked 

 variations, influenced by the character of the food. Similarly, 

 the normal creatinine output in conditions of high muscular 

 activity may be explained by a greater power of the organism to 

 oxidize creatine, although creatine production in these conditions 

 probably exceeds the normal limits. They found, for instance, 

 that only 48 per cent, of ingested creatine reappeared in the 

 urine of a patient who was suffering with continuous tremor, 

 whilst in conditions of atrophy or dystrophy practically 90 per 

 cent, escaped oxidation, and was recovered in the urine. 



More recently still Krause and Cramer, working on the effects 

 of thyroid feeding, find that on a meat-free diet administration 

 of fresh raw thyroid gland is followed immediately by a marked 

 rise in nitrogen excretion, which persists for several days. This 

 increased nitrogen excretion is accounted for by increased urea 

 elimination, and not by an increase in the creatinine elimination. 



Since the effects of thyroid feeding on nitrogen metabolism 

 can be observed in the fasting organism and with a nitrogen-free 

 diet, it would appear that changes in the nitrogen metabolism 

 observed after thyroid administration are due to changes in the 

 tissue or endogenous metabolism. 



According to Folin's view, one would expect to find a marked 

 increase in the excretion of such constituents as creatinine and 

 neutral sulphur, which he believes are the end-products of endo- 

 genous metabolism. The results show, however, that this is 

 not the case, but that the changes induced in the endogenous 

 metabolism of thyroid feeding result almost exclusively in an 

 increased formation and excretion of urea and ammonia. 



In the light of these 'recent researches on the factors which 

 regulate creatinine metabolism, it is evident that the rate of 

 creatinine elimination is not a function of the intensity of cellular 

 katabolism, and is no measure of the total nitrogenous inter- 

 changes taking place within the cells of the different tissues 

 i.e., between the protoplasm of those cells and the nutrient 



