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LEFT VACCINE THERAPY 148 VACUUM discernible for two days. Then a slight papula arises, which, on the 5th or 6th day, becomes of a bluish color and vesi- cular, with a raised head and a central cup. On the 8th day it reaches full de- velopment, and an inflammatory areola appears, which spreads with the exten- sion of the vesicle for two more days. Then a crust or scale is produced in the center of the vesicle, and gradually ex- tends till it covers it in every part. On the 14th or 15th day the scale becomes hard and brown; it next contracts, dries, and blackens, till, between the 20th and the 25th day, it falls off, leaving a per- manent circular, depressed, and foveated cicatrix. Unless it possesses all these characters, and specially unless fovea- tion be present, vaccination is imperfect, and cannot be relied on as a prophy- lactic against smallpox. See Vaccine Therapy. VACCINE THERAPY, BACTERIA THERAPY, the treatment and preven- tion of disease by inoculation with the virus of the bacteria causing the dis- ease. It was first practiced by Dr. Ed- ward Jenner toward the end of the 18th century. ^ He made the discovery that persons inoculated with cowpox were thereby rendered immune against small- pox. Since that time the practice has been extended to s^iveral other diseases, including typhoid fever, asthma, and pneumonia, and it is claimed that in most cases the results have been remarkably successful. Care should be taken to dis- tinguish between Serum Therapy (q. v.) and vaccine therapy. In the former, an- ti-toxins are injected into the blood to assist in the destruction of the toxins which cause the diseased condition. In the latter, bacteria themselves, or their products, are introduced into the blood, the theory underlying the practice be- ing the stimulation of the natural heal- ing powers of the body, by the forma- tion of anti-toxins, thus producing greater resistance to disease. Human serum possesses what Is known as op- sonic action on bacteria, which means that it renders them more easily de- stroyed by the white corpuscles in the blood. ^ The power which the serum of a patient displays toward bacteria is known as the "opsonic index" (see Op- son) and it has been found that when the opsonic index is rising, favorable results can be produced by vaccine in- jection, but when the opsonic index is falling, it is advisable to discontinue injections. VACHELL, HORACE ANNESLEY, an English novelist, born in 1861. He was educated at Harrow and at the Royal Military College, Sandhurst. He became a lieutenant in the Rifle Brigade, in 1883, but later devoted himself to writ- ing. His publications include "7!lomance of Judge Ketchum" (1894); "Model of Christian Gay" (1895); "Quicksands of Pactolus" (1896); "An Impending Sword" (1896) ; "A Drama in Sunshine" (1897); "The Procession of Life" (1899); "John Charity" (1900); "Life and Sport on the Pacific Slope" (1900) ; "The Shadowy Third" (1902); "The Pinch of Prosperity" (1903) ; "Brothers" (1904) ; "The Hill" (1905) ; "The Face of Clay" (1906); "Her Son" (1907); "The Waters of Jordan" (1908); "The Paladin" (1909); "The Other Side" (1910) ; "John Verney" (1911) ; "Jelf's" (1912) ; "Blinds Down" (1912) ; "Bunch Grass" (1912); "Loot" (1914); "Quin- ney's (1914) ; "Spragge's Canyon" (1914); "Searchlights" (1915); "The Case of Lady Camber" (1915) ; "Who Is He?" (1915); "The Triumph of Tim" (1916) ; "Fishpingle" (1916) ; "Humpty Dumpty" (1917) ; "Mrs. Pomeroy's Rep- utation" (1918); "The Soul of Susan Vellam" (1918). VACHEROT, ETIENNE (vash-r6),a French philosopher; born in Langres, France, July 29, 1809; was educated at the Paris Normal School, where he suc- ceeded Cousin as Professor of Philoso- phy in 1839; was dismissed for refusing to take the oath of allegiance when Louis Napoleon became emperor; imprisoned for a year for censuring the Napoleonic system; succeeded Cousin in the Acad- emy of Moral Sciences in 1868; was one of the mayors of Paris during the siege. Was elected to the Assembly, and was one of the three deputies of Paris who voted in favor of making peace with Germany. He wrote a "Critical History of the School of Alexandria" (3 vols. 1846-1851) ; "Democracy" (1859) ; "Met- aphysics and Science" (2 vols. 1858) ; "Essavs in Critical Philosophy" (1864) ; "Religion" (1868)- "Science and Con- science" (1870) ; The External Policy of the Republic" (1881) ; "The New Spirit- ualism" (1884). He died in Paris, July 30, 1897. VACUUM, in physics, a portion of space void of matter. The possibility of the existence of a perfect vacuum has been a favorite subject of discussion among metaphysicians ; and that the neg- ative view was popular is indicated by the historical phrase "the vacuum which nature abhors." Descartes asserted that if the contents of a hollow vessel were taken out without anything entering to fill its place the sides of the vessel would be in contact. This assertion, however, is based on the dogma that the only essential property of matter was its