20 THE PROTEIN ELEMENT IN NUTRITION 



materials of the blood plasma and lymph. It would appear 

 much more probable that the formation of creatine and creatinine 

 represents two phases in the katabolism of one substance, the 

 result of a special process in normal metabolism, as a fall in th?- 

 creatinine output is usually associated with an increased creatine 

 elimination, and a high protein diet (creatine-free), in some 

 patients is accompanied by a rise in the output of both substances. 



It has been shown by Weber that a larger amount of creatinine 

 is to be found in the perfusion fluid when the heart is in action ; 

 whilst, on the other hand, muscular exercise has been confirmed 

 by many observers to cause no rise in the creatinine output. 

 It would, therefore, follow that the creatinine formed in muscle 

 during its activity, and removed from that tissue by the blood 

 is further changed in the organism, only a small fraction of the 

 creatinine of muscle escaping oxidation and appearing in the 

 urine. According to Hoogenhuyze and Verploegh, the power to 

 oxidize creatinine is inherent in all organs. 



It is, therefore, still very doubtful what the origin of creatinine 

 in the body is : whether from the nitrogenous products of the 

 daily food, or by some special process of normal metabolism, 

 according to some observers, probably intimately related to 

 changes in muscle. It is still more doubtful what the fairly 

 constant quantity of creatinine eliminated in the urine is sig- 

 nificant of. There seems to be a general consensus of opinion 

 that it represents an unoxidized fraction of the whole amount 

 formed in the body. There is very little evidence in the more 

 recent researches supporting Folin's view that it represents 

 endogenous metabolism, or that it can be regarded in any way 

 as a measure of the nitrogenous interchanges of the proto- 

 plasmic tissues of the organism. The deductions that have been 

 drawn from his conclusions regarding the origin of creatinine as 

 a product of cellular metabolism can no longer be considered 

 convincing. Thus Folin believes that the constant or endogenous 

 metabolism is largely represented by creatinine, and to a slight 

 extent by uric acid. The deduction from this in Chittenden's 

 words is, considering " these views so admirably worked out by 

 Folin, the question naturally arises, if the real demands of the 

 body for protein food will not be adequately met by the quantity 

 necessary to satisfy the true tissue metabolism." Folin also 

 states in the same connection that only a small amount of 

 protein namely, that necessary for the endogenous metabolism 



