=Silkworm Gut and Silk.=—In plastic surgery silkworm gut and silk are used extensively. Rarely is ordinary catgut resorted to, because it is absorbed before thorough union takes place, besides being a source of infection, either primarily from imperfect sterilization or by taking it up from the secretions of the deeper layer of skin not affected by external antiseptics. The sterilization of silk is accomplished by boiling it for one hour in a 1-20 carbolic solution and then keeping it in a 1-50 similar solution (Czerny). Or it may be boiled in water for one hour and retained in a 1-1,000 alcoholic solution of corrosive sublimate. Ordinarily it may, however, be simply subjected to boiling and steamed in the autocleve. Silkworm gut is treated in the same manner. It has greater tensile strength than silk, and for that reason the thinner varieties are to be preferred to ordinary silk. =Catgut.=—It is far more difficult to prepare catgut, but, since it is necessary for ligation, the following methods may be considered best: The commercial catgut as made from the intestines of sheep, is wound snugly upon a rod of glass and thoroughly brushed with soft soap and hot water. It is then rinsed free of soap, wound upon small glass spools, and placed for forty-eight hours in a one-per-cent alcoholic bichlorid solution, composed of bichlorid of mercury, 10 parts; alcohol, 800 parts; distilled water, 200 parts. The turbid fluid produced by first immersion is changed. Before using, the spools are placed in a glass vessel contain containing a 1-2,000 sublimate alcohol (Schaffer), made up as follows: Bichlorid of mercury gr. vj; Alcohol ℥x; Distilled water ℥iiss. These glass cases are obtainable for the purpose and contain a second perforated compartment for the ligatures passing through rubber valves placed into the openings (Haagedorn). Catgut is generally prepared by soaking in oil of juniper for one week and then retaining it in absolute alcohol (Kocher), or a 1-1,000 alcoholic sublimate solution. Another method for strengthening catgut, as well as to prevent its too rapid absorption, is to chromatize it. This is done as follows: The catgut is placed in sulphuric ether for forty-eight hours, then treated for another forty-eight hours in a ten-per-cent solution of carbolized glycerin, followed by a five-hour subjection to a five-per-cent aqueous solution of chromic acid (Lister). It is allowed to remain in the latter forty-eight hours, then placed in an antiseptic, dry, tightly closed receptacle, and finally soaked in 1-20 carbolic solution before using. The _formaldehyd method_ of Kossman is to immerse the gut in formaldehyd for twenty-four hours, then washing with a solution of chlorid and carbonate of sodium and retaining it in the same solution. The catgut in this procedure swells and its strength is much impaired in this way.