ALBUMINS OR PROTEINS. 235 



acid, and glucuronic acid. The three last compounds unite with a large 

 number of other substances, as is well known, thus protecting the tissue- 

 cells from being attacked. Effort has been made to utilize the above 

 observations as proof of the occurrence of cyanic acid, while, on the other 

 hand, Hofmeister has looked upon it in the light of his assumption of an 

 oxidizing synthesis. We are, therefore, still unable to decide the exact 

 manner in which urea is produced. 



We also desire to call attention to a compound present in urine, although 

 only in small amount, which has often been mentioned in relation to urea. 



This is creatinine: 



NH - CO 

 / 

 C= NH 



\ 



N(CH 3 )CH 2 



The amount excreted daily by human beings varies from 0.6 to 1.3 

 gram. It is the anhydride of creatine, which is present in the muscles, 

 and is a methyl-guanidine-acetic acid: 



NH 2 

 / 



C= NH 

 \ 

 N(CH 3 ) .CH 2 .COOH. 



On boiling with baryta water creatine decomposes, adding water, and 

 forms urea, sarcosin, and other products. It may also be obtained syn- 

 thetically by heating sarcosine (methyl-glycocoll) with cyanamide in a 

 sealed tube to 100 degrees, 1 or by adding a few drops of ammonia in the 

 cold to a saturated solution of sarcosine containing the equivalent amount 

 of cyanamide, and allowing the mixture to stand : 2 

 NH 2 CH 3 NH 2 



CN + N H C = NH 



CH 2 . COOH N (CH 3 ) . CH 2 . COOH. 



Cyanamide Sarcosine Creatine 



Creatine may also be considered a substituted guanidin, as the following 



formula shows: 



NH 2 



\^r 



In 



NH 



H 2 

 Guanidine 



1 J. Volhard: Zeit. f. Chem. 1869, 318. 

 3 A Strecker: Jsb. Chem. 1868, 686. 



