536 PRINCIPLKS OF VETERINARY SURGERY 



structioii. The tissues, at first, exhibit no trace of reaction. 

 A microscopic study of the growth shows a connective tis- 

 sue, with cells hypertrophied and laden with pigment, with- 

 out any evidence of cellular multiplication or alteration of 

 its fibres. This is the maculous melanosis of Gurth. 2nd. 

 When the masses become more voluminous, the infiltrated 

 parts cause an inflammatory reaction of slow development 

 that provokes the formation of a nodule of fuso-celltilar, 

 sarcomatous appearance, in which the pigment continues to 

 accumulate. (Fig. 59). In the course of time the melanic 

 neoplasm is established, the normal structure disappears, 

 and the melanic mass exhibits, on section, the aspect of car- 



Fig. 60. 

 Fibro-plastic Melanotic Tumor (200 diameters) . a. Fusiform Cells Con- 

 taining Black Pigment, b. An Element Completely Infiltrated with 



Pigment. 



bon in which no detail can be distinguished. Washing of the 

 section with a brush removes the infiltrating granules with 

 difficulty. To this form, the name simple m.elanotic tumor 

 may be applied. It is a circumscribed mass in the form of a 

 tumor, the tuberculous tumor of Gurlt. It is the most fre- 

 quent form in the horse. When the masses become too 

 voluminous the pigmentary granules cause destruction of the 

 cells in which they were accumulated, and the lesion then 

 presents the form of a cyst filled with black granules and 

 vestiges of the original tissues. 



The third form more nearly simulates tumors, although 

 it is still simple melanosis. It is habitually found in the 



