CHEMICAL BASIS OF THK ANIMAL KODY. 1305 



acid may be poured into the bottom of a test -tube and the sus- 

 pected fluid carefully added so as not to mix with the acid but 

 float on its surface. If bile-pigments are present coloured rings 

 (layers) appear at the junction of the two liquids, being yellow 

 nearest the acid and progressively red, violet, blue and green 

 j Kissing upwards. It is stated that this test will detect as 

 little as 1 part of bilirubin in 70,00080,000 parts of solvent. 



2. Biliverdin. 1 C 16 H 18 N 2 O 4 . 



This is, as already stated, the first product of the oxidation 

 of bilirubin. It gives the characteristic colour to the bile of 

 herbivora, probably accounts for the colour of biliary vomit in 

 carnivora (man), is possibly found in the urine in icterus, has 

 been stated to occur in the edges of the placenta in pregnant 

 animals (bitches), while on the other hand it occurs in mere 

 traces in gall-stones whether of man or other animals. It has 

 also been described as occurring in egg-shells and the integu- 

 ments of certain invertebrates. 



Apart from its colour biliverdin differs most characteris- 

 tically from bilirubin in its solubilities. It is (like bilirubin) 

 soluble in alkalis but insoluble in water and ether, whereas 

 (unlike bilirubin) it is insoluble in either chloroform, carbon- 

 bisulphide or benzene, but readily soluble in alcohol and in 

 glacial acetic acid. It has further never been obtained in a 

 crystalline form, and like bilirubin it shews no absorption bands 

 but a somewhat strong absorption of the violet end of the 

 spectrum. Treated with fuming (yellow) nitric acid it gives 

 Gmelin's reaction, starting now with a blue colour as a product 

 of the first stage of its oxidation. 



3. Bilicyanin. (Cholecyanin, Choleverdin.) 



This is the substance which results from the oxidation of 

 biliverdin and is the cause of the blue colour observed when 

 bile is treated with fuming (yellow) nitric acid as in Gmelin's 

 reaction. 



Bilicyanin is for practical purposes characterized solely by 

 its marked absorption spectrum. This consists of three bands, 

 one on each side of Z), that to the red side of D being the 

 darkest, and one between b and F. The latter is probably 

 identical with the band seen in acid solutions of eholeteliu and 

 due to the production of this substance in small quantity during 

 the oxidation of bilirubin. The position of the bands varies 

 somewhat according to the solvent employed and as to whether 

 the solution is acid or alkaline. 



During the application of Gmelin's test for bile-pigments the 

 1 The formula here given should probably be doubled. 



