PRINCIPLES OF VETERINARY SURGERY 533 



for the points of predilection, where melanic pigment is usu- 

 ally deposited reveals the fact that the connective tissue 

 is a favorite location, but that certain organs, like the liver, 

 spleen, etc., may be affected, and, finally, that any of the tis- 

 sues or organs may at times harbor melanism. 



The connective tissue is the seat of predilection for mel- 

 anic deposits. It has shown elsewhere that its formative 

 elements accumulate more particularly in tissues that have 

 the same blastodermic origin, and, since the connective tis- 

 sue is distributed over the entire body, the varied locations 

 of melanism are clearly explained. The pigment may be con- 

 veyed by the blood or by the elements which have formed 

 it. The claim that it always locates at the seat of neoplasms 

 is not true, for, in fact, the pigment is most frequently de- 

 posited in the absence of new formations. Investigations 

 and observations, based on the dissection of old animals in 

 veterinary schools during a long period, emphatically estab- 

 lish this fact. Indeed the frequency of melanosis in the horse 

 does not correspond with the rareness of true tumors. Out 

 of 1,700 horses slaughtered. Bard found but three real tu- 

 mors, while melanosis was found in every tenth horse. And, 

 finally, melanosis does not cause cachexia in the horse. 



Moreover, microscopic examinations have shown that 

 melanic tumors often contain no other organization except 

 the connective tissue in which the pigment is deposited. 

 Most frequently there is no trace of new formation. This 

 statement does not, however, imply that fibromata, sarco- 

 mata, carcinomata, etc., are not sometimes impregnated 

 with melanosis. The truth is that these tumors may, like 

 any other tissues, be impregnated with melanin, yet pigment 

 masses of the tail, anus and perineum may at a late period 

 be found associated with a fibroma that contains no pigment. 

 With these facts as a basis, two varieties may be distin- 

 guished : 



