424 TUMOURS. 



are similar in form to white blood corpuscles, but containing 

 granules of dark pigmentary matter, which give the tumours 

 their characteristic black appearance. 



The dark granules of pigment not only fill the cells, but lie 

 free in the surrounding fibres, as shown in Fig. 98. 



Melanosis has hitherto been described as a benign disease in 

 the lower animals, both by human and veterinary pathologists. 

 Professor Spence says — " The melanotic cancer has this pecu- 

 liarity, that a form of it occurs in the lower animals which cannot 

 be distinguished from the black cancer in man. But in the 

 former case it is not malignant, and has no tendency to return 

 after removal, while in the human subject it is plainly and 

 entirely a malignant disease — a melanotic form of cerebriform 

 cancer." Paget says — " In the horse and dog, I believe, black 

 tumours occur which have no cancerous character; but none 

 such are recorded in human pathology." 



I have seen a great many cases of melanosis, but I never saw 

 one in the horse, the history of which I could afterwards trace, 

 where the disease did not return ; and if recurrence only were 

 the special characteristic of malignancy, this would prove the 

 true nature of the growth, without a shadow of doubt. But a 

 malignant is not the only growth that is liable to recur, hence 

 the recurrent character of melanosis can only be taken as one 

 fact to prove its malignity. 



I have also seen melanosis in horned cattle of various colours, 

 but more particularly in those of a dark brown or black colour, 

 and as a rule early removal has been effectual, and there has 

 been no recurrence. 



A melanotic tumour has all the specialities of malignancy. Ist. 

 Its minute structure is not like any of the fully-developed natural 

 parts of the body. 2d. It is usually an infiltration; and this 

 characteristic is much more manifest than in medullary cancer ; 

 although it may appear as separable masses, it will be found, 

 on close examination, that the structures surrounding the tumour 

 are deeply tinged with the pigmentary matter, and that they 

 gradually disappear either by absorption or by being appropriated 

 as materials for the growth of the malignant disease. 3d. It 

 has a tendency to enlarge, not only by growth, but apparently 

 by multiplying itself in the formation of other tumours around 

 it, or in more remote parts of the body. 4:th. Ulceration in 

 melanosis is as constant as in the other malignant tumours. 



