58 PIGMENTATION. 



tlius removed, when retained in the gall-bladder for any length 

 of time, it undergoes further changes, passing through shades 

 of yellow, grey, brown, and black, which Stddeler terms respec- 

 tively hilifuscin (Cso^ioo^ 2^8)7 hiliverdin (CgaHgoNaOio), Uli- 

 2?msin (CgoHooNoOia) ^nd hili]iumin\ bilifuscin differing from 

 bilirubin in containing two atoms more HO, biliverdin from bili- 

 fuscin in containing two atoms more 0, biliprasin from biliverdin, 

 again, by an access of 2 HO, wdiilst bilihumin is a black, in- 

 soluble, very highly oxidised substance. 



§ 56. The scale of colours enumerated above serves, as 

 already stated, as a standard for the course of all other chroma- 

 toses, wdiether physiological or pathological. The former, to 

 which I can only allude by the way, are due to the fact that 

 certain other cells either possess, like those of the liver, or obtain 

 with the lapse of years the powder of appropriating the blood- 

 pigment dissolved in the serum, and of condensing it in their 

 interior ; among these may be enumerated the epithelial cells of 

 the choroid and the rete Malpighii, and certain ganglion-cells. 

 The black pigment found in the lungs deserves to be considered 

 separately. I have already called attention (in a note to § 46) 

 to the ease with which particles of vegetable charcoal (especially 

 wood charcoal) become imbedded in the lungs, where they may 

 be mistaken for pigment-granules. Hence I am not disposed to 

 deny that a certain small proportion of the lung-pigment may 

 be due to the accidental admission of carbonaceous particles. 

 The probability of this is enhanced by the obstinate resistance 

 which the pulmonary pigment offers to the action of reducing 

 agents, a fact which leads us to infer that it must, at all events, 

 contain a very large proportion of pure carbon. Moreover, the 

 observation that the pigmentary particles of the lungs are occa- 

 sionally found enclosed in cells can no longer be held to invali- 

 date the coal-dust theory, inasmuch as it has recently been 

 demonstrated that cells of soft consistency, e.g, colourless blood- 

 corpuscles, may take up minute particles of solid matter into 

 their protoplasm. Notwithstanding all this, however, it is only 

 a small proportion of the lung-pigment wdiich can be regarded 

 as consisting of charcoal particles introduced from without, the 

 remaining part being unquestionably derived from the colouring* 

 matter of the blood. The proof of this is to be found, on the 

 one hand, in the anatomical similarity between this and other 



