292 . LECTURE XIII. 



has recently called our attention to the importance of considering the 

 muscles as a source of purine bases, and, consequently, they are related 

 to the formation of uric acid. He showed in the first place that the endo- 

 genous uric acid elimination in human beings during twenty-four hours 

 was not appreciably influenced by muscular activity, whereas hourly 

 values were distinctly changed. Vigorous muscular exertion is followed 

 by an hour of increased elimination of urinary purine. This increase, 

 during the time of work, does not influence the uric acid, as such, but 

 principally the purines. The noticeable increase in uric acid elimination 

 is only evident some time later. By a subsequent diminution of the uric 

 acid and purine eliminations, the daily uric acid and purine values are 

 practically unaffected by periods of rest or of activity. Naturally such 

 investigations can be carried out only when no food is eaten, or at least 

 none containing purine, or the amount of purine bases in the food must be 

 definitely known. Burian finally, in order to establish more closely the 

 relations of the muscles to purine metabolism, caused blood to flow through 

 the surviving muscles of a dog. It was found first of all that the liquid 

 which was originally perfectly free from uric acid always contained it after 

 a short time. If the muscle was stimulated, purine bases appeared in 

 considerable quantity, and chiefly hypoxanthine. The discovery is also 

 very important that the amount of hypoxanthine in the muscle itself is 

 greatly increased when it is tetanized. From this we must assume that 

 the muscle, when at rest, constantly oxidizes hypoxanthine to uric acid. 

 When its metabolism is increased by greater demands upon it, the muscle 

 cells are no longer able to oxidize all of the purine bases, and especially 

 the hypoxanthine, so that then unchanged hypoxanthine is given up to 

 the blood. It is very important that according to these observations the 

 muscle cells are constantly forming hypoxanthine. These investiga- 

 tions are not to be regarded, however, as perfectly conclusive. We have 

 mentioned them here because from them we may perhaps expect to obtain 

 the first explanation of the part played by the purines of the food in 

 cellular metabolism, and concerning the extent of the synthetic formation 

 of purine bases. 



We have been informed recently concerning the breaking down of the 

 individual purine bases to uric acid, and their subsequent fate in the animal 

 organism, by a series of valuable experiments by A. Schittenhelm. 1 They 

 have been confirmed by further observations by Richard Burian. 2 We have 

 already mentioned the fact that Horbaczewski could detect the formation 

 of uric acid in the pulp of organs, or in extracts of them, in the pres- 

 ence of oxygen. It was now found possible to follow carefully the 



1 A. Schittenhelm: Z. physiol. Chem. 42, 251 (1904); 43, 228 (1904); 45, 121, 152, 

 161 (1905) ; 46, 354 (1905). 



2 R. Burian: Z. physiol. Chem. 43, 497 (1905). 



