ALBUMINS OR PROTEINS. 233 



acid in large amounts from the urine of human beings and dogs after the 

 administration of milk of lime. Furthermore, it has been observed that 

 dogs with an Eck's fistula showed severe indications of poisoning, and that 

 the same symptoms could be obtained by the introduction of carbamates 

 into the blood-stream. This method of proof is not convincing. Macleod 

 and Haskins * have recently indicated the normal presence of carbamates in 

 the urine and of an increased appearance after extirpation of the liver. 

 We must admit that the estimation of the carbamic acid was only an 

 indirect one. On the other hand, the formation of carbamates corre- 

 sponds very well with the assumption of the production of urea from 

 ammonium carbonate, as previously mentioned. We wish to emphasize, 

 however, that its normal occurrence and its relations to the production of 

 urea have not yet been absolutely proved. 



It will be appropriate at this point to call attention to the observa- 

 tion of M. Siegfried, 2 which may have some bearing on the formation of 

 urea as indicated above. M. Siegfried found that when carbon dioxide 

 was led into a mixture of equal parts of normal glycocoll and baryta 

 solutions no immediate precipitation of barium carbonate appeared, as 

 was to be expected, but the mixture remained clear for some time. It 

 gradually became turbid on standing. In studying this subject further, 

 Siegfried found that salts of the following type were formed: 



R N' 



| X COOH 

 COOH 



Siegfried analyzed several of these salts, for instance, calcium glycocoll- 

 carbonate (calcium carbamoacetate) : 



/ H 

 CH 2 N COO 



COO Ca/ 



Also the calcium alanine-carbonate (calcium carbamopropionate) : 



CH 3 



C NH COO 



COO Ca/ 

 The composition of calcium leucine-carbonate is: 



(CH 3 ) 2 . CH . CH 2 . CH . NH . COO 



COO Ca 



1 Am. J. Physiol. 12, 444 (1905). 



2 Z. physiol. Chem. 44, 85 (1905); 46, 401 (1905). 



