104: IMMEDIATE PKINCIPLES OF THE TISSUES. 



product varies much in composition, and abounds in carbon 66 to 

 72 per cent. (Schmidt?) Melanine occurs in the black serum which 

 has sometimes been observed. 



Melanine is, doubtless, derived from hasmatine. In the choroid 

 coat it contains .254 per cent, of iron. (Lehmann.) It occurs within 

 all pigment cells, in the form of granules; and in other cases, espe- 

 cially in melanotic tumors, it is also found scattered among cells or 

 tissues. In the choroid coat of the eye this pigment is, doubtless, 

 subservient to vision. For other particulars, see the section on 

 "Pigment-cells." 



Having thus completed the description of the immediate princi- 

 ples of which the solids and fluids of the human body are composed, 

 we next enter upon Histology proper. 



