201 ANAESTHETICS.—ANILINE.
latter solution is then gradually added to the formertill a permanent precipitate is produced. Sufficientpotash solution is then added to make the fluidmeasure 100 c.c.
The test glasses should be colourless and of equalsize. They should be marked at 100 c.c., and themark should be at the same height in each cylinder.
The process is carried out thus :—The solution tobe tested is placed in one of the cylinders, made upto 100 c.c. 'with water, and T5 c.c. of Nessler’ssolution mixed with it by means of a pipette. Thetint produced is carefully observed, and then imi-tated as nearly as possible by running into the othercylinder as many tenths of a c.c. of ammonia as it isimagined will produce the same effect. The secondcylinder is then filled up to 100 c.c. with water, 1-5c.c. of Nessler’s solution added, and after allowingthe whole to stand a few minutes, the tints of thecontents of the two cylinders compared. If not alike,a fresh experiment is necessary. When the solutioncontains more than 1 mgrm. of ammonia in 100 c.c.,the tint produced is far too dark for correct estimation.
ANESTHETICS (French , anesthesiques; from a priv.,and aiaHavoiAcu, to feel) is the name given to certainsubstances which, when introduced into the circula-lation, are capable of depriving the patient of thepower of motion and of sensation. These agentsare now largely used in therapeutics and in den-tistry, for producing insensibility to the pain neces-sarily attendant upon surgical operations, and alsoas remedial agents in certain diseases characterizedby great excitement of the sensorial functions.
Although it had long been known that narcotics,when administered in sufficiently large doses, pro-duced coma and insensibility, the use of anaestheticsfor the alleviation of pain is of comparatively recentdate. An American, Dr. Jackson, first suggestedtheir use in 1840, and immediately afterwards theywere successfully employed in dentistry by Dr.Morton, and also by the American surgeons, War-ren, Biglow, and Hayward. On the 19th ofDecember in the same year Liston, the eminentsurgeon, and Mr. Kobinson, a dentist, operated onpatients rendered insensible by the inhalation ofether vapour. In 1847 ether was employed inEngland and in France , and towards the endof that year Flourens pointed out the anaestheticproperties of chloroform; to Dr. Simpson of Edin-burgh , however, we are indebted for the intro-duction of the use of chloroform in surgical andobstetrical practice. Dr. Snow in 1849 published awork on the inhalation of ether, and also discoveredthat amylene was capable of producing effects similarto those of chloroform ; the latter, however, is nowalmost invariably used in surgical operations, as itsaction is much more rapid than that of ether. Amy-lene is intermediate in rapidity of action betweenchloroform and ether; but as two out of the fewcases in which it was tried proved fatal, its use wasdiscontinued. Methylene dichloride, also, has recentlybeen recommended by Dr. Richardson as an anaes-thetic, but it has the disadvantage of causing greatdepression.
These agents are administered through the respira-tory organs by inhaling the vapour mixed with air.For this purpose some of the chloroform is pouredon to a sponge or handkerchief, which is then appliedto the mouth and nostrils of the patient in such amanner that the air which passes into his lungs issaturated with the vapour. Ether is administeredin the same way. Dr. Snow , who has paid muchattention to this matter, invented a special form ofapparatus for inhaling the vapour.
The first effect produced by the administration ofthe anmsthetic agent is a species of intoxication causedby its action on the cerebral lobes, and as this actionextends to the cerebellum the patient becomesincapable of directing his movements—a resultsimilar to that of alcoholic intoxication. In the nextstage the spinal cord is attacked, unconsciousnesssupervenes, and all powers of motion and sensationare lost. The individual is now said to be in a stateof anaesthesia; but the heart beats, breathing con-tinues, and the other essential functions of the bodyare carried on. If, however, the exhibition of theanaesthetic agent is still continued, the temperatureof the body becomes lowered, the movements ofrespiration and circulation become impaired, theheart ceases to beat, and death finally ensues.
The introduction of anaesthetics into surgicalpractice has greatly contributed to its progress: thepatient being motionless and free from pain, theoperator is enabled to perform with much greaterdelicacy and readiness; moreover, in the reductionof dislocations and of hernia, the muscles beingflaccid, the obstacle produced by their contractionis removed.
M. Velpeau endeavoured to produce localanaesthesia, or insensibility of that part of the body tobe operated on, by means of a refrigerating mixtureof ice and salt; it was, however, found to be veryunmanageable. Since then local anaesthesia has beensuccessfully obtained by means of a spray of etherdirected upon the part; the intense cold producedby the rapid evaporation of the ether entirely de-priving it of sensation.
See Chloroform, Ether, and Nitrous Oxide orlaughing gas, for methods of preparation and pro-perties. Various other agents, such as amylene,ethyl chloride, ethyl nitrate, benzene, and carbonbisulphide, "have been proposed as anaesthetics; butfrom their injurious effects they have never beenbrought into use.
ANILINE AND ANILINE DYES—Aniline. Theterm Aniline, or Aniline oil, is used commercially toindicate a variable mixture of bodies, amongst whichcertain members of the series of organic bases knownas the Aniline homolognes greatly preponderate. Anil-ine itself, the parent member of this series, is indi-cated by the formula C 6 II 6 ,NII 2 ; the formulae of allthe true liomologues of aniline are deducible fromthis parent symbol by substituting for one or moreof the five II symbols in the radical Cgll- a corre-sponding number of univalent hydrocarbon radicalsof the methyl series, just as the formula) of benzeneliomologues are deducible from the symbol of benzene