Chloroform, or Terchloride of Formyle, is a volatile liquid which is analogous to Ether and Alcohol both in nature and medicinal action, but very different in chemical construction. Ether = C_{4}H_{5}, O. Alcohol = C_{4}H_{5}, O+HO. Chloroform = C_{2}H, Cl_{3}. A solution of Chloroform in spirit, sold under the names _Terchloride of Carbon_ and _Chloric ether_, is in very general use, and is employed in very much the same cases as Nitric ether, being in the first place stimulant, and subsequently anodyne, soporific, and diaphoretic. Chloroform is physiologically an Inebriant. But it is for certain peculiar actions that are coincident with, or immediately follow, this production of inebriation, that it has been so widely and so successfully employed in medicine since its recent discovery. Its two important operations are its anæsthetic effect on sensory nerves, and its paralyzing influence on muscle. With regard first to the general selection of anæsthetic or anodyne remedies, it is to be observed that there are four distinct kinds of Pain, which differ very much in the treatment required. (1.) Firstly, there is _inflammatory_ pain, caused by an active disease. It is aggravated by pressure; and it has a local cause. For this Opium is the best Neurotic remedy, but it should not be used without an attempt being previously or at the same time made to subdue the active inflammation. (2.) _Irritative_ pain is different. It depends merely on nervous irritation. It also has a local origin; but it is relieved, instead of being aggravated, by a pressure or friction. Such is the pain produced by lead-colic, or by the passage of a gallstone or renal calculus. The pain of Neuralgia is generally of the irritative kind. So is that of Gastrodynia. So also the pain artificially inflicted by the knife in surgical operations. For irritative pain on the surface Aconite is most efficacious. Belladonna comes next to it. In Gastrodynia Hydrocyanic Acid is to be preferred. But to counteract the pain of a surgical operation we require a medicine which shall be capable of producing a powerful effect on the whole system at once. Such medicines are Ether and Chloroform. It is found most convenient to bring the patient under their influence by causing him to inhale the vapour into his lungs. Being absorbed by the pulmonary mucous surface, and passing directly into the circulation, the medicine thus takes effect rapidly. There is no time for the volatile liquid to be excreted from the blood, so that the ulterior effect of the anæsthetic cannot be escaped. The third and most important advantage of this mode of administering Chloroform is that by it we are enabled to regulate with exactness the degree of its action, which is a dangerous one, and to stop it when it has gone far enough. When introduced by inhalation into the general circulation, Chloroform acts upon the brain and sensory nerves throughout the body,