270 PYOCYANIN. 



to the secretions or organs in which they occur, to their genetic 

 relationships each with the other, or in some cases (lipochromes) to 

 their probable chemical similarities. But in addition to these an 

 extremely numerous mass of pigments has been at different times 

 described under various names, as obtained from the brightly-coloured 

 parts of invertebrates and of vertebrates, such as the feathers, &c. 

 Our knowledge of them is quite incomplete and limited in most cases 

 to statements of their solubilities and the absorption spectra which 

 some of them yield. In most cases nothing is known of their chemical 

 nature or their relationships (if any) to each other, and any description 

 of them, even if it were profitable, is impossible within any reasonable 

 limits. 



For details and references to the literature of the several pigments see Gamgee, 

 Physiological Chemistry, Vol. i. 1880, p. 305, and particularly Krukenberg, Ver- 

 gleichend-physiol. Studien, Heidelberg, 1881 1888 and Vergleich. physiol. Vortrage. 

 Bd. i. 1886, Nr. 3. 



In conclusion it must suffice to describe two pigments which do not 

 naturally fall under any of the above groups into which these substances 

 have been divided. 



Pyocyanin 1 . Pus, which ordinarily presents a more or less bright 

 yellow colour, is frequently greenish and sometimes blue. The blue 

 colour is due to a pigment (pyocyanin) which is apparently formed 

 in the pus by the action of specific organisms. It is obtained either 

 from pus or the bandages into which it has been absorbed by extraction 

 with dilute alcohol or with water to which a trace of ammonia has 

 been added. The alcoholic extract is then evaporated to a small bulk 

 and the residue extracted with chloroform, or it may be extracted 

 at once from the aqueous solution by shaking with chloroform. It 

 may be obtained in a crystalline form by slow evaporation of the 

 chloroformic solutions, the crystals being readily soluble in water and 

 alcohol, but only slightly in ether. Acids change the blue colour 

 to red and alkalis restore the original blue. None of the solutions 

 show any distinct absorption bands. When kept the crystals turn 

 greenish, due to a decomposition which takes place most readily in 

 alkaline solutions exposed to the air and light, and results in the 

 formation of a yellow pigment, pyoxanthose. The latter is, unlike 

 pyocyanin, only slightly soluble in water but readily soluble in ether, 

 by which property the two pigments admit of being separated. 

 Pyoxanthose is crystalline, soluble in alcohol and chloroform, is 



1 Fordos, Compt. Rend. T. LI. (1860), p. 215 ; Ibid. LVI. (1863), p. 1128. Liicke, 

 Arch. f. klin. Chirurg. Bd. in. (1863), S. 135. Girard, Deutsch. Zeit. f. Chirurg. 

 Bd. vii. (1876), S. 389. Fitz, Ber. d. d. chem. Gesell. Bd. xi. (1878), Sn. 54, 1893. 

 Kunz, Monatsh. f. Chem. Bd. ix. (1888), S. 361. 



