310 COLOURING MATTERS. 



identical with melanin, is a question which, with our present very 



imperfect knowledge of this pigment, must still remain undecided. 



Virchow found these crystals to be flat rhombic tablets with 



extremely acute angles. 



Composition. Scherer* gives the following as the mean result 



of three analyses of this body : 



Carbon 58'084 



Hydrogen 5*917 



Nitrogen 13768 



Oxygen 22-231 



100-000 



As we are neither acquainted with the atomic weight of this 

 body, nor with any of the products of its decomposition, we cannot 

 attempt to construct a hypothetical formula for it. In the pigment 

 from the choroid coat of the eye 1 found 0*254^ of iron. 



The black pigment which is often deposited as a morbid product 

 in the lungs presents great differences of composition. In two 

 different cases which C. Schmidtf analysed he found : 



Carbon 72-95 6677 



Hydrogen 475 7'33 



Nitrogen 3'89 8'29 



Oxygen 18'41 17'6l 



100-00 100-00 



Preparation. The best method of obtaining this body is from 

 the eye, by removing the retina, and detaching the choroid coat 

 from the sclerotic. The choroid coat must be placed in a clean 

 rag, and the colouring matter washed out with pure water, just as 

 the starch-granules in the preparation of gluten are washed out 

 through linen bags; the pigment remains for a long time suspended 

 in the water, from which, however, it may be readily removed by 

 filtration, or the fluid may be evaporated and the residue extracted 

 with water. 



Tests. The physical properties of this body are so character- 

 istic, that it is easy to recognise and to separate it; generally, 

 however, it only occurs in such small quantities that it is impos- 

 sible to distinguish whether the object in question is identical with 

 the melanin of the eye, especially as we still know comparatively 

 little regarding the chemical characters of this last-named sub- 

 stance. No conclusions regarding the presence of black pigment 

 can be drawn from mere colour and insolubility in different men- 



* Ann. de Ch. u. Pharm. Bd. 40, S. 6. 



*fr Vogel's pathol. Anat. S. 161 [or English Translation, p. 192.] 



