392 PHYSIOLOGY 



CHAP. 



has not been detected at all in muscle, it might reasonably be 

 assumed that most of the creatine of the muscles is converted 

 into urea, and given off into the blood in proportion as it is formed, 

 to be eliminated from the blood with the urine by the kidneys. 

 But the fact, as demonstrated by Meissner (1865, 1866, 1868), that 

 the whole of the creatine ingested, or injected into the veins, 

 passes into the urine without conversion into urea, contradicts this 

 opinion, as maintained by some physiologists. Bunge, however, 

 holds that although the creatine introduced into the body is 

 not converted into urea, this does not prove that such a conversion 

 does not occur in the creatine formed by muscle, since muscle 

 only picks up the nutrient substances from the blood, and not the 

 katabolites artificially introduced into the circulation, such as 

 it habitually excretes into the blood. He thinks it highly 

 probable that creatine is a mother substance of urea, more 

 particularly as creatine contains three atoms of nitrogen and 

 only four atoms of carbon. 



These hypotheses of Bunge do not appear to us to be com- 

 patible with Baldi's investigations (1889), carried out in our 

 laboratory upon Succi during his fasts. Baldi found that the 

 creatinine never entirely disappeared from the urine between the 

 1st and 30th days of fasting, but that it diminished in proportion 

 with the total nitrogen of the urine. If the urea is derived from 

 the creatine, then during inanition, when the organism is living 

 at the expense of its own tissues, the creatine should be entirely 

 converted into urea and disappear from the urine. If it does not 

 disappear even when the nitrogen of the urine is reduced to a 

 minimum of 3 grms. per diem, but keeps in almost constant ratio 

 with the urea, this implies that the latter is formed (at least 

 mainly) by processes which are entirely independent of the con- 

 version of creatine. 



Although creatine has been synthetically obtained by Volhard 

 and by Strecker from the combination of sarcosine with cyanamide, 

 it has not yet been artificially produced by cleavage of the different 

 proteins. By the hydrolytic cleavage, with acids, of caseinogen, 

 conglutin, gelatin, and other proteins the compound arginine has 

 been obtained, which is homologous with creatine and creatinine 

 (C 4 H 7 N 3 0). Both from creatine and arginine urea is split off on 

 boiling with baryta water. This shows that the whole of the urea 

 may not be formed synthetically after oxidation, but that part 

 of it may be formed by hydrolytic cleavage from either creatine or 

 arginine. 



A large part of the creatinine of the urine of man and carnivora 

 comes directly from the creatine of the alimentary flesh. Another 

 part is formed from the katabolic processes in the muscles of the 

 body, which, as stated above, contain a considerable amount of 

 creatine. The urine of herbivora also contains creatinine, like the 



