REACTION

n. Re-ak's hu3n. Lat., reactio. Fr., reaction. Ger.,.R., Gegenwirkuny (1st def.). 1. An action or motion resulting from and opposed to another action or motion. In Newton's third law of motion, the word r. designates the effect produced upon a moving body by its own motion as distinguished from "action," the effect which it produces upon other bodies. The word hence denotes mutual action, interaction. 2. In chemistry, a physical phenomenon occurring on the application of a chemical test, and hence indicative of the po e ion of a special chemical property; also, a physical phenomenon indicative of a change in the chemical state of a body; hence the change of state itself, whether this is brought about by the molecular interaction of two or more substances or the application of a physical force. 3. In electrophysiology, a physical phenomenon occurring upon the application of electricity and indicating therefore the po e ion of certain electrical properties or some change in electrical condition. [B.] 4. The proce of recovery from "shock." [E.] 5. The development of fever as the result of an injury, a surgical operation, or the like. Acid r. 1. A r. indicative of acidity, such as the reddening of blue litmus-paper by the action of an acid. 2. The po e ion of acid properties. [B.] Adamkiewicz's r. A r. used as a test for albuminous bodies. On di olving the substance to be tested in glacial acetic acid and gradually adding concentrated sulphuric acid, the presence of albuminous bodies causes a violet coloration and slight fluorescence. [B, 270 (a, 38).] Alkaline r. A r. indicative of alkaline properties, such as the turning of red litmus paper blue by an alkali. [B.] Amphicroitic r., Amphigenous r., Amphoteric r., Amphoterous r. A combination of acid and alkaline r. shown under certain conditions, when substances stain red litmus-paper blue and blue litmus-paper red. This occurs occasionally in the urine. [B.] Biuret r. Ger., Biuretprobe. A r. by which a solution of copper sulphate and an exce of caustic soda produce a reddish or deep-violet color (according to the amount of copper sulphate) when brought into the presence of biuret or of albuminous substances, nucleins, etc. [B, 270 (a, 38).] Chemical r. See R. (2d def.). Electrical r., Galvanic r. See R. (3d def.). Galvano-tropic r. A phenomenon observed by L. Hermann in small aquatic animals placed in a ve el through which a galvanic current is made to pa . After a few violent movements they place themselves in the direction of the galvanic current, with the head directed toward the anode, and remain motionle while the current is pa ing. [Pfluger's "Arch.," xxxvii, p. 457; "Ctrlbl. f. d. med. W nsch.," Apr. 24, 1880, p. 291 (B).] Ginelin's r. A r. shown by biliary matter when 3 or 4 parts of urine are put into a conical gla ve el, and 1 part of a mixture of equal amounts of 25-per-cent. nitric acid and red fuming nitric acid is poured slowly down the side of the ve el. Green, blue, violet, and yellow colors form where the acid collects at the bottom, [a, 34.] Gruppenr' (Ger.). A chemical r. common and peculiar to a group of substances, indicating that the substance tested belongs to that group. [B, 270.] Hemiopic pupillary r. Of Wernicke, a r. observed in hemianopsia in which a pencil of light thrown on the blind side of the retina produces no r. in the iris, but thrown on the normal side of the retina produces binocular contraction of the pupils. ["N. Y. Med. Jour.," Dec. 31, 1887, p. 750 (a, 34).] Hydrochloric-acid r. The a umption of a violet color by albuminoids when boiled with crude fuming hydrochloric acid. [B.] I so faradaic r. Of Adamkiewicz, a condition of a muscle in which it reacts to faradization, but not to galvanism. [" Charit6 Ann.," 1878, v, p. 353 (a, 34\] Myotonic r. Of Erb, a r. observed in Thomson's disease, in which the faradaic excitability is increased quantitatively and qualitatively. The changes are not unlike those observed in the r. of degeneration, the stabile currents producing rhythmical, wave-like contractions. ["N. Y. Med. Jour.," Aug. 14, 1886, p. 188 (a, 34).] Neutral r. Fr., reaction neutre. Ger., neutrale R. A r. indicative of the absence of both of two opposite positive qualities; usually of the absence of both acidity and alkalinity. [B.] II. of degeneration. The electrical r. indicative of degenerative changes in a nerve. It consists in a rapid lo of the galvanic and faradaic irritability of the nerve itself and of the faradaic irritability of the muscles supplied by it, while the galvanic irritability of the muscles increases and remains exalted for a number of months (until muscular atrophy supervenes). [B.] R.- time. The time which elapses between the reception of a stimulus by a nerve-centre and the emi ion of the consequent motor impulse. [B.] Xanthoproteic r. A r. seen on adding strong nitric acid and then ammonia to a solution containing a proteid. A characteristic orange-color results. [K.] [s. 383]