THE DIAMINO-ACIDS. 87 



On decomposition with strong hydrochloric acid indicau is accord- 

 ingly decomposed into sulphuric acid and indoxyl, which latter can 

 then be oxidized to indigo-blue : 





Indoxyl. Indigo-blue. 



On reduction indigo-blue is transformed into indigo-white, 

 C 8 H 6 NO, which, when boiled with zinc and water, then further 

 yields indol : 



C 8 H 5 NO + H -= CgHeNO. 



CgHeNO + 3H r- C 8 H 7 N + H 2 O. 



Animal indican must not be confused with vegetable indican, 

 which is a glucoside, and yields indigo-blue and indiglucin on 

 hydrolytic decomposition : 



C 26 H 31 NO 17 + 2H 2 O = C 8 H 5 NO + 3C6H 10 O 6 

 Vegetable indican. Indigo-blue. Indiglucin. 



A small amount of skatoxyl, indoxyl, and phenol is also eliminated 

 in the urine, in combination with glucuronic acid, as skatoxyl, 

 indoxyl, and phenol glucuronates, respectively. This acid may be 

 derived from glucose by the substitution of one atom of oxygen for 

 two atoms of hydrogen, and is accordingly represented by the 

 formula COOH.(CH.OH) 4 .COH. On oxidation it is transformed 

 into saccharinic acid, the relation of which to glucose has already 

 been considered. 



Glucosamin (chitosamin) occupies a position intermediary between 

 the amino-acids and the carbohydrates. It is an amino-hexose and 

 has the formula : CH 2 (OH).[CH(OH)] 3 .CH(NH 2 ).CHO. It is the 

 mother-substance from which chitose is built up and which is 

 found extensively among invertebrates. The relation existing 

 between the two is seen from the equations : 



(1) CH 2 .OH.[CH.OH] 3 .CH.NH 2 .COH + 40 = 



CH 2 .OH[CH.OH],.COOH -f HNO 2 

 Chitonic acid. 



(2) CH 2 .OH[CH.OH],.COOH + 2H = 



CH 2 .OH[CH.OH] 4 .COH + H 2 O 



Chitose. 



II. THE DIAMINO-ACIDS. 



The diamino-acids which have been obtained upon hydrolysis of 

 the albumins are arginin, lysin, and diamino-trioxydodecanic acid. 

 The two former are diamino-monocarbonic acids ; the latter is a 

 diamino-oxymonocarbonic acid. Together with arginin and lysin 

 histidin is frequently found, and for some years it also was regarded 



