Though intense cold produces pain, and at first increases the sensitiveness of the part to painful impressions, as to that of a blow for example, yet after a time it completely benumbs the nerves, and quite suspends sensibility. This happens, in a considerable degree, before positive freezing takes place, and always completely afterwards. ice is sometimes employed for this purpose, in the relief of neuralgic pains. When these are superficial, ice or ice-cold water, applied so as to produce a benumbing effect, will sometimes afford relief, and may be tried when other measures have failed. Dr. Arnott has found the frigorific mixture, applied so as to freeze the surface, often promptly successful in headache, toothache, and neuralgia of the face, side, and other parts, though it has often also failed. {Ed. Month. Journ. of Med. Sci., July, 1854, p. 37.) But it is rather as a surgical anaesthetic that extreme cold has recently attracted notice. To Dr. James Arnott, as before stated, the profession is indebted for this application of cold; and it is certainly an important addition to our therapeutic resources. The following remarks on the method of using it, and its effects, are taken mainly from the communications of Dr. Arnott.

The frigorific mixture used consists of two parts of powdered ice and one of fine table salt. For most purposes, four ounces of ice, or a piece about as large as an orange, will be sufficient. This should be thoroughly comminuted by shaving with a plane, or pounding it in a bag of canvas or coarse cloth, and then placed on a sheet of paper, and mixed quickly and intimately with the salt, by means of an ivory folder, or by stirring the two in a gutta percha vessel. The mixture thus prepared is to be introduced into a net of gauze, which may be conveniently suspended for the purpose from the mouth of a jar; and, as soon as drippings of brine begin to appear, it is ready for use. The net enclosing it is now to be applied to the part horizontally placed, and, if not large enough to cover the surface which it is wished to affect, is to be passed quickly from one part of it to another, so as to operate on the whole equably. The liquid which escapes may be received upon a wet sponge, or in a basin placed beneath.

Dr. Arnott has recently proposed what he considers an improved method of producing the impression of external cold upon the surface. instead of directly applying the frigorific mixture, he effects the same purpose by introducing a piece of metal, iron, copper, or brass, for example, of suitable size and shape, into the mixture, and, when it has become of the same temperature, removing it, and bringing it immediately into contact with the part to be frozen. A small flat-iron, such as is used in laundries, will answer in many cases. When time is required, two of these instruments may be used, one being kept in the mixture while the other is applied. A thin metallic bottle of tinned iron or aluminium, filled with the freezing mixture, will serve the same purpose; and sometimes a Florence flask might answer. (Med, T. and Gaz., June, 1863, p. 584 ) When only a small surface is to be operated on, the use of a thin metallic spoon containing a portion of the mixture has been suggested.

A certain degree of numbness is immediately produced, and the skin rendered pale, with little disagreeable sensation even of coldness in half a minute, the whole surface is suddenly blanched, and a feeling of tingling or pricking is experienced like that caused by mustard. if the application be continued, the adipose matter becomes solidified, and the whole tissue hardened, with a slight tingling pain, which, however, except in peculiarly sensitive parts, as the hand, and anterior and lower part of the forearm, is rarely complained of. This uneasiness soon subsides, and perfect insensibility takes place. The time required for producing the effect varies with the condition of the surface. if this be perfectly sound, not more than one or at most two minutes will be necessary; if inflamed, as in an abscess, from six to ten minutes may be required. The insensibility remains for many minutes after the re- moval of the mixture. The part, when insensibility is no longer required, should be gradually restored to its normal condition by covering it with pounded ice, or a bladder containing ice and water. This will not be required in cases in which the refrigerating process is checked before the freezing effect has been produced. Upon the thawing of the part, some redness and dilatation of the blood-vessels may result; but this, so far from being inflammation, is a state of debility, which permits distension through the vis a tergo. in fact, the part is, under these circumstances, quite indisposed to take on inflammation, generally, if cut, heals kindly by the first intention in twenty-four hours, and never suppurates; nor does inflammation occur in the neighbouring parts. Dr. Arnott asserts that he has never known any injury result from the process, and his statement is confirmed by others. There is not the least danger of gangrene.

The resulting hardness is quite different from that of frozen water, as it is only the fatty matter that is consolidated; the blood being driven out by the contraction of the vessels. it can be cut readily, but requires that the knife should be held somewhat more firmly in the hand than in the ordinary condition of the tissue. There is, of course, no hemorrhage from the frozen parts. For slight operations it is not necessary to produce the full freezing effect.

As the congelation does not penetrate more deeply than the skin and the adipose tissue immediately subjacent, the measure is not calculated to obviate the suffering from extensive operations; except in so far as it renders perfectly painless the first incision through the skin, which is usually the most painful part of the cutting. it is more especially the smaller operations to which this anaesthetic measure is appropriate; but, as these are much more numerous than those of greater importance, its beneficial influence will be widely felt, if all that it promises should be fulfilled. it is perfectly safe, and thus has an incalculable advantage over chloroform, which has frequently caused death, when employed in cases to which the present measure is adapted.