The instruments necessary to operate in this case are a very sharp convex bistoury, a pair of clamps, some strong twine, a castrating forceps and a pair of scissors. The clamps are wooden or metallic pincers, formed to embrace the cord and to be applied firmly upon it, in order to hold it securely, and to confine the artery tightly enough to prevent the occurrence of hemorrhage. The form most ordinarily used, and probably most convenient, is made of wood, and consists of two semi-cylindrical pieces (Fig. 10) joined at one end and resting together by a flat and sometimes grooved surface, and measuring about six inches in length. The material is a light but strong wood. They are rounded at the extremities, in order to avoid chafing the soft tissues. A groove at each end is designed to receive the twine, which is part of the appliance. Before being used they are tightly tied together at one end, in such a manner that they spring open if closed. This point is one of the first importance. It requires considerable exercise of strength to place them tightly enough on the cord they are to hold, but this firm juxtaposition, so obtained, facilitates their removal, when that is required. The groove which they carry on their flat surface is sometimes filled with some merely lubricating greasy substance, usually simple ointment, fresh lard, butter, or cream, though some veterinarians use a caustic paste. This last mode of proceeding is strongly opposed by some authorities, as likely to induce unnecessary inflammatory action, through the formation of a scab, which may require for its removal a process of sloughing, which may in some cases give rise to serious complications. As I have stated, the clamps are not always made of wood, and very many alterations and improvements, so called, have been from time to time brought forward. In Fig. 11 a few of these clamps are presented. The oldest form is the simplest, and possesses the further advantage of being always easy to be obtained, while the more complicated contrivances are not always easy of access. [Illustration: FIG. 11. VARIOUS SHAPES OF CLAMPS. Screwed Clamp. Spring Clamp of Brandt. Hinge Clamp.] [Illustration: FIG. 12. FORCEPS TO HOLD THE CLAMP TOGETHER. VISE FOR THE SAME.]