108 SPINDLE-CELL SARCOMATA. 



tlio cellular elements are normally infiltrated with a certain 

 amount of pigmentary matter. Pigmentation is usually explained 

 by supposing that the morbid growth inherits the vital pecu- 

 liarities of those cells from which it sprang. But this doctrine 

 must not be too rashly accepted. The metastatic deposits, which, 

 owing to the well-marked malignity of the melanotic sarcoma, 

 are by no means rare, exhibit the same disposition to pigmentary 

 infiltration, though developed in parts where no physiological 

 pigmentation is known to occur. This transfer of a purely 

 local peculiarity to the secondary tumours has been advanced 

 both for and against the doctrine in question. For it, by those 

 who hold that metastasis is caused by the transfer of material 

 elements from the primary tumour to other parts ; against it, by 

 the believers in a constitutional dyscrasia which generates black 

 tumours, where it generates any tumours at all. 



We ought, in my opinion, to distinguish as clearly as we 

 •can between the two following points : 1st, the exciting of the 

 metastatic deposit by cells which have migrated from the primary 

 tumour ; and 2nd, the pigmentation of the secondary tumour. 

 AVith regard to the former, I refer the reader to the hypotheses 

 and scruples enunciated in § 120; with reference to the latter, it 

 must be understood that all the cells of a melanotic eirowth are 

 originally colourless. No one will assert that they are directly 

 descended from cells which have migrated from the primary 

 tumour ; on the contrary, their local origin is beyond all ques- 

 tion ; and as they nevertheless become pigmented, we must 

 needs ascribe their pigmentation to a constitutional tendency 

 Avhicli is independent of the seat of origin of the primary tumour. 

 Etiological experience accords with this view ; it teaches us that 

 an over-production of pigment is, at all events in the skin, a 

 l)redisposing element in the causation of these tumours. This 

 over-production manifests itself either in the growth of black 

 Avarts which may degenerate directly into melanotic sarcomata, 

 or in a black or brown staining of the skin, whether diffuse or 

 circumscribed. The special predisposition of creatures totally 

 devoid of pigment, e.g. of white horses, to become affected by 

 melanotic sarcoma, may be explained on the theory of a vicarious 

 j)igmcntation, the deposit occurring at a single point, and being 

 therefore associated with a certain degree of tissue irritation. 



In all melanotic tumours the cells are the exclusive deposi- 



