It is impossible to particularize the nature of every =tumor= to which the horse is subject, such formations being so very various. Seldom are two cases met with in which a precisely similar structure is developed. More seldom are two cases encountered located upon the same part. These growths are liable to every possible change. One may be very small, but extremely malignant, or of that kind which seems to resent the slightest interference. Employ the knife to this last sort, and incurable ulceration may start up. All remedies may be powerless and the life may be sacrificed. Such growths are, happily, rare in the equine species; but the author has heard of their occurrence, although it has not been his misfortune to encounter one. Another shall be of such enormous size as to impede the motions, yet will be perfectly bland in its nature. A portrait, not of the largest tumor which the writer has witnessed, but of the most awkwardly situated, is represented herewith. It was not malignant. The horse which carried about this burden was brought to the veterinary college during the time when the author was attached to that establishment. The animal had previously been under the treatment of various veterinary surgeons. All had cut and cauterized the enlargement, but without reducing its magnitude. The wounds healed quickly, and the constitution appeared not to be in the slightest manner affected. Why was not the swelling removed with the knife, when the kindly nature of the growth had been ascertained? For good and sufficient reasons. No operation could, with the slightest prospect of success, be hazarded. In the first place, nature is apt to resent the loss of so large a substance, or, in other words, although the surgery may be perfect, the life, from some unexplained cause, is likely to depart before the operation is finished. In the next place, most bland tumors, when of magnitude, are of a semi-cartilaginous nature, and spring either from tendon or from bone--usually from the latter. This tumor impeded the action; hence it was inferred that the substance ramified among the fibers of the pectoral muscles. Those fibers are large, and are divided; they present interspaces, between which the abnormal growth might readily penetrate. Now, unless every portion of the tumor were excised, the enlargement would sprout again, and the surgeon would be disgraced. To remove the pectoral muscle of a man, would be esteemed of little consequence, so that the life was preserved. But the limbs of the horse constitute the value of the creature's existence and to disable these from being safely moved, would be to return a burdensome life to the proprietor. Therefore that which is compatible with human surgery could not be entertained in veterinary science.