PRINCIPLES OF VETERINARY SURGERY 531 



erns the transformation of coloring matter into melanin, and 

 how the multiplication and functional superactivity of the 

 pigmentary cells occur. It is well established that the chro- 

 matoblasts of certain inferior animals, — the lizard and the 

 frog, — are directly dependent upon the nervous system, and 

 that those of mammals are also governed by the nerves. It 

 is, therefore, easy to conceive that the trophic influence of 

 a lesion of a nerve center can provoke general hypertrophy 

 of the pigmentary cells. Pathological pigmentation is in fact 

 only an exaggerated and perverted normal pigmentation. 



It has been established that the white color of hair con- 

 stitutes a predisposition to melanosis. From an etiological 



Fig. 58. 

 Cells in the Different Phases of Pigmentation. 

 a, b, c, e. Cells of a Pigmented Cancer. 

 d, Pigmented Epithelium of a Blood Vessel. 



point of view it should be known that melanic products are 

 generally found in animals having coats more or less depig- 

 mented, and, according to observations of Arabs, in animals 

 that have wavy and woolly manes and tails. But on this point 

 it might be asked whether the tumor led to curliness or 

 whether it is a state directly connected with melanic alter- 

 ations. In order to explain the formation of melanotic tu- 

 mors in animals with coats of light color, Trasbot resorts to 

 the melanogenic ( ?) power, which, not being sp£nt, is kept 

 in reserve, and at a given moment begins to accumulate. 

 But knowing the rapidity vnth which imused elements are 

 eliminated from the body, the theory cannot be defended. 

 Besides, although it is true that the white horse is chiefly 



