ANALGESICS. Agents that diminish pain. These may be either agents that are applied locally, and exert their influence on the ends of the sensory nerves ; or they may be remedies which are given internally and either act on the centres of consciousness in the brain, benumbing the sense of pain, or exert their influence on the sensory end-organs through the medium of the blood-vessels. In the former class belong those that act on the skin and those that act on the mucous membrane, many of which are very widely used in medicine at the present day. As the skin does not absorb very readily, acting usually only through its sweat-glands, many analgesics which are extremely effective when applied to the mucous surfaces have little or no action on the skin. Cocaine is an excellent illustration of this general principle.
Of the analgesics that are used on the skin, cold and heat are of immense importance. Ice-bags and hot-water-bags are very useful in reducing the pressure of inflammation, thus indirectly alleviating pain. Freezing mixtures, such as ethyl chloride, etc., are highly efficacious in causing local analgesia, and these mixtures are frequently employed to render the skin insensible, so that minor operations can be performed without pain.
A large number of aromatic compounds, particularly combinations of phenol, of menthol, of thymol, etc., are of immense service in relieving pain by local application. Thus, oil of wintergreen, which is so very widely utilised for local neuralgias and for muscular, affections resembling rheumatism, is one of these aromatic compounds, being methyl salicylate, which is closely related to carbolic acid.
Another class of remedies that are utilised as local analgesics on the skin are the various preparations of belladonna, particularly ointments and plasters. Belladonna has the property of destroying the sensibility of the ends of the sensory nerves in the skin, which accounts for its efficacy in neuralgias and painful affections of the muscles, such as lumbago. backache, stiff neck, etc.
The local analgesics most widely used on the mucous membranes are cocaine and its allies. The action of these agents on the inflamed mucous surface is rapid, but very evanescent, and it should never be forgotten that the relief from pain is often gained at the expense of acquiring a lifelong and destructive habit. Within recent years a number of closely related com
pounds have been used for local analgesics on mucous surfaces, eucaine, holocaine, etc., being examples. In addition to these a number of benzoic acid derivatives have also been widely employed, and have the great value of being more persistent in action and less liable to induce a habit. These local analgesics for the mucous membrane are of particular value in inflamed conditions of the nose and throat, especially in tuberculous laryngitis and in ulcer or cancer of the stomach.
Of the analgesics that are used internally it may be said that it is fortu nate that medicine has at its command a large variety. Whereas in ancient times opium was almost the only pain-destroying remedy which the physician possessed for internal medication, he now has at his command twenty or thirty excellent remedies for producing the desired result. Naturally, opium stands at the head of the line as the most effective pain-annulling remedy. But its use is attended with great gers, and countless lives are sacrificed on the altar of morphine and opium habits.
Of the newer analgesics, antipyrine, acetanilide, phenacetine, and their allies represent the most important groups. These are particularly valuable in the treatment of neuralgic affections, head ache, tnenstruation pains, influenza pains, and the various pains in muscles and joints which result from acute and chronic rheumatism, etc. Their use is attended, however, with constant danger ; and many instances of severe poisoning and even death are recorded from the too free and indiscriminate taking of these remedies. They are quite dissimilar in their action in certain indi viduals, and no layman should dose himself with them or with any of the many headache-powders and pain-destroying remedies that are so widely placed on the market. The great danger that is caused by these drugs, particularly by acetanilide, and in a less degree by the phenetidines, is the destruction of the red blood-cells. This is an accident \rhich is often very serious.