The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Techniques for staining cells in order to improve their study had been developed as early as the late seventeenth century. Antoni van Leeuwenhoek had found that the addition of saffron dye to cells helped to distinguish certain features of those cells. The invention of synthetic dyes by William Perkin in the 1850s greatly increased the number of colored compounds available for cell staining, while the work of Robert Koch, Walther Flemming, and Paul Ehrlich expanded and improved cell-staining techniques
An important breakthrough in cell-staining methods occurred in 1884, when Danish bacteriologist Hans Christian Joachim Gram (1853-1938) introduced a new technique to the field. Improving on a method originally developed by Ehrlich, Gram found that conventional stains could be washed off some bacterial cells, but not others. In his technique, Gram first treated bacteria with an aqueous solution of gentian violet in aniline, then with a solution of iodine in potassium iodide. When the bacteria were next washed with alcohol, some retained the original stain, but others lost their color. The former have come to be known as gram positive bacteria and the latter as gram negative bacteria.
Gram's technique has become a standard method for classifying bacteria. In recent years, bacteriologists have learned that antibiotic activity tends to correlate with this system of classification. For example, gram positive bacteria are sensitive to penicillin, while gram negative bacteria are more effectively treated with streptomycin.