CHEMICAL BASIS OF THE ANIMAL BODY. 1317 



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, 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 organ- 

 isms. 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 alco- 

 holic 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 chloro- 

 formic 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 shew 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, pyoxan- 

 those. 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 crys- 

 talline, soluble in alcohol and chloroform, is coloured red by 

 acids and violet by alkalis. Since pyoxanthose appears to be a 

 product of the decomposition of pyocyanin, both pigments may 

 occur simultaneously in pus, in which case the fluid is green. 

 According to some more recent observations pyocyanin as 

 judged of by its reactions with the chlorides of gold and 

 platinum and with other alkaloidal precipitants, as also from 

 the formation of crystalline compounds with acids, is closely 

 related to the alkaloids. 



Sweat is also occasionally coloured blue, in some cases by 

 indigo-blue (p. 1282) as in urine, and it may be (?) by a pig- 

 ment similar to pyocyanin. 



Pigment of the suprarenal bodies. A suprarenal body when 

 a section is made through it is found to consist of an outer or 

 cortical portion, of a yellow colour, which constitutes the chief 

 part of its structure, and an inner, medullary part of a darker 

 colour. When the latter is acted upon by ferric chloride it 

 assumes a. dark bluish- or greenish-black colour, and if an 

 aqueous extract of its substance (or the tissue itself) be treated 

 with an oxidizing agent it turns red. It appears therefore that 

 the suprarenals contain some form of chromogen or pigment- 

 forerunner which gives rise under appropriate conditions to 

 a pigment. According to some observers extracts of the 

 cortex shew a spectrum similar to that of the histohsematins 



