Melanoid Or Pigmented Sarcoma always originates in a situation where pigment already exists, the eye or skin. The cells of which it is composed are usually spindle-shaped, but may be round, and from the first they tend to the aggregation of brown or black pigment in their substance (Fig. 102). The pigment is very irregular in its distribution. In a melanotic tumour there may be portions unpigmented, and even in the pigmented parts some cells are free from pigment. The melanotic sarcomas have a great tendency to metastasis, and as the material is conveyed by the blood there are pigmented tumours formed in a great variety of organs and tissues where they may grow to great dimensions, though the original tumour may be very small.

It is necessary to distinguish from these proper melanotic sarcomas those which become pigmented from blood. In the former the pigment is brown or black from the first, being obviously elaborated by the cells. In the latter the 'pigment is red or yellow, and the pigmentation may be related to a special weakness of the vessels allowing of haemorrhage.

The term Chloroma has been applied to a form of round-celled sarcoma of a peculiar greenish-yellow or grass-green colour. It occurs primarily in the periosteum of the face and head, and may lead to secondary tumours of similar colour in the liver, kidneys, etc. The colour is due to small refracting granules which appear to be composed of fat.