368 PHYSIOLOGICAL CHEMISTRY. 



tion appears to take place in transfusion experiments with 

 creatine, and it has been shown that creatine introduced with 

 the food appears in the urine, not as urea, but as creatinine. 

 On the other hand, it is possible that the change may take place 

 in the muscles, where the store of creatine is the greatest, and 

 the urea, as fast as formed, may pass into the blood to be later 

 eliminated in the urine, while the other residue undergoes 

 further oxidation. The portion of the muscular creatine 

 which is not so changed, as a source of energy, appears in the 

 urine as creatinine in the main. In presence of acids a mole- 

 cule of water is lost and the anhydride results : 



NH 



H 2 / \ 



CH 3 -*- H - N=C \ N CH> + H 2 



1N CH 2 .COOH CH 3 



But in alkaline solution the reverse reaction takes place, crea- 

 tine being formed. Creatinine may be separated from the 

 urine most easily with zinc chloride as a crystalline double salt 

 \vhich is yellow because of the coprecipitation of pigments; 

 when purified the crystals are colorless. Creatinine is found 

 in normal amount in the urine of vegetarians. Toward cop- 

 per and other metallic solutions it behaves as a reducing agent 

 when alkali is present. 



CARBOHYDRATES. 



Normally no large amount of any carbohydrate passes from 

 the blood into the urine, but with increased sugar concentra- 

 tion in the blood from any cause, the urine may contain sugar 

 in more than traces. When sugars are consumed in more 

 than the " assimilation limit " a part of the excess may be 

 found in the urine. This is true of glucose as well as of cane 

 sugar and maltose. 



But under normal conditions there is evidence that traces 

 of several carbohydrates and of bodies related to them pass 

 also into the urine. It is well known that the a-naphthol reac- 

 tion is given with ordinary normal urines, and this points to 



