VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 33 



bone or soft parts, by which means they have a cavity in them ; a structure pe- 

 culiar to this kind of cuticular substance. 



Incysted tumors in different animals would appear, from these observations, to 

 be confined in their production to the cuticular substance proper to the animal in 

 which they take place; for, though cuticle, hair, nail, hoof, and horn, are 

 equally productions of animal substance, only differing in trivial circumstances 

 from each other, we do not find in the human subject any instance of an incysted 

 tumor containing a substance different from the cuticle, hair, and nails of the 

 human body, to which last the horny excrescences, the subject of the present 

 paper, are certainly very closely allied, both in growth, structure, and external 

 appearance; and when of some length, they are found to be so brittle as to 

 break in two, on being roughly handled, which could not happen either to hoof 

 or horn. In the sheep they produce wool instead of hair; and in one instance 

 in that animal, where they give rise to a horny excrescence, it was less compact 

 in its texture, and less brittle than similar appearances in the human subject; on 

 being divided longitudinally, the cut surface had more the appearance of hoof, 

 and was more varied in its colour, than nail. 



Incysted tumors being capable of producing horns, on the principle we have 

 laid down, is contrary to the usual operations of nature; for horns are not a pro- 

 duction from the cutis, and though not always formed on a bony core, but fre- 

 quently on a soft pulp, that substance differs from common cutis in its appear- 

 ance, and extends a considerable way into the horn: it is probable, that this pulp 

 requires a particular process for its formation*. The cases of horns, as they are 

 commonly termed, on the human head, are no more than cuticular productions 

 arising from a cyst, which in its nature is a variety of those tumors described by 

 Mr. Hunter under the general name of cuticular incysted tumors-^. These in- 

 cysted tumors, when considered as varieties of the same disease, form a very 

 complete and beautiful series of the different modes by which the powers of the 

 animal economy produce a substitute for the common cuticle on parts which have 



• A sheep, about 4 years old, had a large horn, 3 feet long, growing on its flank. It had no 

 connection with bone, and appeared to be only attached to the external skin. It dropped off in con- 

 sequence of its weight having produced ulceration in the soft parts to which it adhered. On examining 

 it, there was a fleshy substance, 7 inches long, of a fibrous texture filling up its cavity on which the 

 horn had been formed. — Orig. 



t The principle on which the production of these excrescences depends being once explained, the 

 modes of preventing their formation, and removing them when formed, wUl be readily understood, 

 the destruction of the cyst being all that is required for tliat purpose. This may be done before the 

 tumor opens externally, or even after the excrescence has begun to shoot out, and will be better 

 effected by dissection than escharotics, since the success of the operation depends on the whole of the 

 bag being removed. — Orig. 



VOL. XVII. F 



