The pigmentary granules of the negro's skin and hair can be freed in several ways from the cells in which they are lodged and collected in any desired amount.
As thus obtained, these granules are found to be insoluble in dilute alkalies, dilute hydrochloric acid (hot or cold), alcohol, or other organic solvents when applied in the order named. If, after they have been subjected to the action of dilute hydrochloric acid, they are again treated with dilute alkalies, they are found to give up their pigment, and, on the continued application of heat, the granules dissolve entirely in the alkaline solution, leaving only an insignificant residue.
The pigmentary granules are composed of a colourless ground substance or substratum, a pigment, and much inorganic matter. Their inorganic constituents, as thus far determined, are calcium, magnesium, iron, and silicic, phosphoric, and sulphuric acids; and these constituents possibly play an important part in the deposition and fixation of the colouring matter in the granules.
The pigment isolated from the granules, and sufficiently freed from adherent inorganic matter, contains only the merest trace of iron—so little, in fact, that we must think of it when entirely pure as free of iron. Heating the isolated pigment with barium hydrate at a temperature of 260° C. entirely frees it from the closely adherent ground substance, and it is then found that the vapours of pyrrol are no longer emitted when it is subjected to dry distillation, and the odour of burnt feathers is no longer discerned, although nitrogen is still present.
We can not conclude as the result of our work that the pigment is a derivative of hæmoglobin; it seems to us more probable that it is ultimately derived from the proteids of the parenchymatous juices.
The total quantity of soluble pigment in the skin of a negro of average size is found to weigh about 1 gramme; the weight of the pigmentary granules is about 3.3 grammes, if we are right in our assumption that they contain sixty-five per cent of water and five per cent of mineral constituents in their natural state in the epidermis.
The pigments of the epidermis and hair of the negro are very likely identical. In the present state of our knowledge we can only say that it seems highly probable that the pigment of the negro's hair is not different from the dark pigment found in the hair of the white races, and we may infer that the pigment of the black skin differs only in amount and not in kind from that deposited in the skin of the white man.