•78 MAN'S PHYSICAL WELFARE by his fellow-dentist Wells, to demonstrate the use of ether in surgical operations. Morton had already used it with success in extracting teeth. Ether is the common name for diethyl ether, (C2H5)20. It may be prepared by the action of sulfuric acid on ethyl alcohol. Ether has been the main general anaesthetic for many years because it gives good relaxation, and the margin of safety between a useful plane of anaesthesia and a dangerously deep one is reasonably wide. Ether is far from being an ideal anaesthetic, however, because of the severe depression following its use and the metabolic disturbances it produces. Like all inhalation anaesthetics, ether is irritating to the respiratory tract, and ether anaesthesia is sometimes followed by pneumonia. Other Advances in Anaesthesia Quickly Followed the Discovery of Ether Anaesthesia. A year after the discovery of ether anaesthesia, James Simpson introduced the use of chloroform. Chloroform is not tolerated as well as ether as a rule, and it damages the liver. The use of chloroform as a general anaesthetic in surgery is less frequent than the use of ether in the United States. Its noninflammability, however, makes it peculiarly useful in restricted fields (e.g., in operations when a cautery is used). In 1923 Dr. Arno Luckhardt found that ethylene gas was superior to ether in that it was less irritating to the respiratory tract and produced less postoperative nausea. The use of an ethylene-oxygen mixture has replaced ether in many hospitals. Acetylene gas is also a general anaesthetic, but it is not used because of its objectionable odor. Divinyl ether has recently come into use as a general anaesthetic for short operative procedures. Tribromethyl alcohol is supplied in the United States as "avertin with amylene hydrate"; it produces anaesthesia when introduced into the rectum. CH2 About 1935 cyclopropane H2C CH2 came to be recognized as an excellent general anaesthetic because of its comparatively low toxicity and its satisfactory relaxation. Dr. H. R. Griffith reported, "My conception of anaesthesia with the older gases is that we administer the gas plus enough oxygen to keep the patient alive and in good condition. With cyclopropane, on the other hand, w^e administer oxygen with just enough of the anaesthetic gas to keep the patient asleep." For many years hypnotics have been used prior to giving a general anaesthetic.
C RELIEF OF PAIN REVOLUTIONIZED SURGERY 779 Local Anaesthetics Are Used When General Anaesthetics Are Unnecessary. Local anaesthetics are superior to general anaesthetics for manypurposes because they influence only the area of the operation and do not leave such undesirable aftereffects as nausea, acidosis, and pneumonia. Local anaesthetics may be injected into tissues, or they may be applied directly to surfaces such as in the eye, ear, nose, and throat. When the Spaniards conquered Peru, they noted that the Indians reduced their sensitivity to pain by chewing the leaves of the coca plant. In 1859 the German chemist, Wohler, isolated the alkaloid cocaine from these leaves, but it was not until 1884 that Carl Roller first used it as a local anaesthetic in the surgery of the eye. Although cocaine is an excellent local anaesthetic, it possesses the two disadvantages that it is quite toxic and habit-forming. Cocaine was analyzed and its structural formula determined. Soon a number of simpler substances having structural resemblance to cocaine were prepared. Among these were the /3-eucaine, stovaine, and alypin, but these substances gave way to procaine ("novocaine") in 1906. Procaine is less toxic than cocaine and is not habit-forming. Procaine solutions are stable, while solutions of cocaine are not stable. Unfortunately, procaine does not produce anaesthesia when placed directly on such tissues as the eye, nose, and throat. Many synthetic compounds have been prepared and tried out in recent years. Among them, butyn, which resembles procaine in structure, may be used for direct application. Butyn produces anaesthesia more rapidly and gives more prolonged anaesthesia than either cocaine or procaine. 0=( H— H CH3 C—CHa